Invitation Only Research Event

Research Event

15 April 2020

23 April 2020

The actin cytoskeleton is extremely dynamic and supports diverse cellular functions in many physiological and pathological processes, including tumorigenesis. However, the mechanisms that regulate the actin-related protein 2/3 (ARP2/3) complex and thereby promote actin polymerization and organization in cancer cells are not well-understood. We previously implicated the proline-rich 11 (PRR11) protein in lung cancer development. In this study, using immunofluorescence staining, actin polymerization assays, and siRNA-mediated gene silencing, we uncovered that cytoplasmic PRR11 is involved in F-actin polymerization and organization. We found that dysregulation of PRR11 expression results in F-actin rearrangement and nuclear instability in non-small cell lung cancer cells. Results from molecular mechanistic experiments indicated that PRR11 associates with and recruits the ARP2/3 complex, facilitates F-actin polymerization, and thereby disrupts the F-actin cytoskeleton, leading to abnormal nuclear lamina assembly and chromatin reorganization. Inhibition of the ARP2/3 complex activity abolished irregular F-actin polymerization, lamina assembly, and chromatin reorganization due to PRR11 overexpression. Notably, experiments with truncated PRR11 variants revealed that PRR11 regulates F-actin through different regions. We found that deletion of either the N or C terminus of PRR11 abrogates its effects on F-actin polymerization and nuclear instability and that deletion of amino acid residues 100–184 or 100–200 strongly induces an F-actin structure called the actin comet tail, not observed with WT PRR11. Our findings indicate that cytoplasmic PRR11 plays an essential role in regulating F-actin assembly and nuclear stability by recruiting the ARP2/3 complex in human non-small cell lung carcinoma cells.

Incorporation of ribonucleotides into DNA can severely diminish genome integrity. However, how ribonucleotides instigate DNA damage is poorly understood. In DNA, they can promote replication stress and genomic instability and have been implicated in several diseases. We report here the impact of the ribonucleotide rATP and of its naturally occurring damaged analog 1,N6-ethenoadenosine (1,N6-ϵrA) on translesion synthesis (TLS), mediated by human DNA polymerase η (hpol η), and on RNase H2–mediated incision. Mass spectral analysis revealed that 1,N6-ϵrA in DNA generates extensive frameshifts during TLS, which can lead to genomic instability. Moreover, steady-state kinetic analysis of the TLS process indicated that deoxypurines (i.e. dATP and dGTP) are inserted predominantly opposite 1,N6-ϵrA. We also show that hpol η acts as a reverse transcriptase in the presence of damaged ribonucleotide 1,N6-ϵrA but has poor RNA primer extension activities. Steady-state kinetic analysis of reverse transcription and RNA primer extension showed that hpol η favors the addition of dATP and dGTP opposite 1,N6-ϵrA. We also found that RNase H2 recognizes 1,N6-ϵrA but has limited incision activity across from this lesion, which can lead to the persistence of this detrimental DNA adduct. We conclude that the damaged and unrepaired ribonucleotide 1,N6-ϵrA in DNA exhibits mutagenic potential and can also alter the reading frame in an mRNA transcript because 1,N6-ϵrA is incompletely incised by RNase H2.

In bacteria, the restart of stalled DNA replication forks requires the DNA helicase PriA. PriA can recognize and remodel abandoned DNA replication forks, unwind DNA in the 3'-to-5' direction, and facilitate the loading of the helicase DnaB onto the DNA to restart replication. Single-stranded DNA–binding protein (SSB) is typically present at the abandoned forks, but it is unclear how SSB and PriA interact, although it has been shown that the two proteins interact both physically and functionally. Here, we used atomic force microscopy to visualize the interaction of PriA with DNA substrates with or without SSB. These experiments were done in the absence of ATP to delineate the substrate recognition pattern of PriA before its ATP-catalyzed DNA-unwinding reaction. These analyses revealed that in the absence of SSB, PriA binds preferentially to a fork substrate with a gap in the leading strand. Such a preference has not been observed for 5'- and 3'-tailed duplexes, suggesting that it is the fork structure that plays an essential role in PriA's selection of DNA substrates. Furthermore, we found that in the absence of SSB, PriA binds exclusively to the fork regions of the DNA substrates. In contrast, fork-bound SSB loads PriA onto the duplex DNA arms of forks, suggesting a remodeling of PriA by SSB. We also demonstrate that the remodeling of PriA requires a functional C-terminal domain of SSB. In summary, our atomic force microscopy analyses reveal key details in the interactions between PriA and stalled DNA replication forks with or without SSB.

Histone H2B monoubiquitylation (H2Bub1) has central functions in multiple DNA-templated processes, including gene transcription, DNA repair, and replication. H2Bub1 also is required for the trans-histone regulation of H3K4 and H3K79 methylation. Although previous studies have elucidated the basic mechanisms that establish and remove H2Bub1, we have only an incomplete understanding of how H2Bub1 is regulated. We report here that the histone H4 basic patch regulates H2Bub1. Yeast cells with arginine-to-alanine mutations in the H4 basic patch (H42RA) exhibited a significant loss of global H2Bub1. H42RA mutant yeast strains also displayed chemotoxin sensitivities similar to, but less severe than, strains containing a complete loss of H2Bub1. We found that the H4 basic patch regulates H2Bub1 levels independently of interactions with chromatin remodelers and separately from its regulation of H3K79 methylation. To measure H2B ubiquitylation and deubiquitination kinetics in vivo, we used a rapid and reversible optogenetic tool, the light-inducible nuclear exporter, to control the subcellular location of the H2Bub1 E3 ligase, Bre1. The ability of Bre1 to ubiquitylate H2B was unaffected in the H42RA mutant. In contrast, H2Bub1 deubiquitination by SAGA-associated Ubp8, but not by Ubp10, increased in the H42RA mutant. Consistent with a function for the H4 basic patch in regulating SAGA deubiquitinase activity, we also detected increased SAGA-mediated histone acetylation in H4 basic patch mutants. Our findings uncover that the H4 basic patch has a regulatory function in SAGA-mediated histone modifications.

This MPI Europe webinar examines innovative ways to better design and implement predeparture orientation programs for resetttling refugees. The discussion features observations from a refugee who went through an orientation program before being resettled in the Netherlands, and a resettlement agency official in Norway.

As the U.S. health-care system sags under the strain of the COVID-19 pandemic, health-care workers are not only on the frontlines fighting the virus, they are also some of the most at-risk individuals, making it more essential than ever to have sufficient numbers of qualified health professionals. While 1.5 million immigrants and refugees are already working in the U.S. health-care system, an additional 263,000 immigrants and refugees in the U.S. with health-related college degrees are working in low-skilled jobs or are out of work.

The White House immigration plan offered as a solution to resolve the fate of DREAMers seeks legal immigration cuts unlike any seen since 1924. In addition to a decrease of up to 40 percent in family-sponsored immigration, the proposal demands vast increases in enforcement and a retrenchment in protections for those seeking humanitarian relief. In exchange, one-sixth of the unauthorized population could gain legal status.

Marking the release of MPI President Andrew Selee's latest book, speakers explore emerging trends in migration, economic interdependence, technology innovation, and cultural exchange that are transforming the relationship between the United States and Mexico, and the policy implications of these changes for the future.

The number of international students enrolled in U.S. colleges and universities has risen steadily since the mid-20th century. Today, the United States represents the top destination for international students worldwide. Learn more about where these students come from, which universities they attend, and the subjects they study in this Spotlight article.

A report release and presentation of first-ever U.S. estimates on the actual economic costs of skill underutilization for immigrants, their families, and the U.S. economy, in terms of forgone earnings and unrealized federal, state, and local taxes.

More than 1 million international students were in the United States in 2015-16, a significant share of them in science, technology, engineering, or math (STEM) fields. While countries increasingly are vying for this population, these individuals face a complex choice upon graduation: to stay or leave? This article examines international STEM students in the United States and the motivations underlying their postgraduation plans.

In 2015, 43.3 million immigrants lived in the United States, comprising 13.5 percent of the population. The foreign-born population grew more slowly than in prior years, up 2 percent from 2014. Get sought-after data on U.S. immigration trends, including top countries of origin, Mexican migration, refugee admissions, illegal immigration, health-care coverage, and much more in this Spotlight article.

Immigrants from India are the second-largest foreign-born group in the United States, after Mexicans. Indian immigrants tend to be far more highly educated and have greater English proficiency than the foreign-born population overall. This Spotlight article offers the latest data on Indian immigrants, focusing on population size, state- and city-level distribution, occupation, educational attainment, and more.

The Chinese represent the third-largest immigrant population in the United States, their numbers having grown rapidly in recent decades. The population is atypical in some respects: Far more highly educated and likely to have come via student and employment pathways than the overall U.S. foreign-born population. This article offers key data on Chinese immigrants, including top destinations, incomes, and English proficiency.

During its first year, the Trump administration methodically put in place a series of bureaucratic barriers that could significantly reduce opportunities for foreigners to come to the United States legally. Among the actions taken during 2017: Imposition of a much-challenged travel ban suspending the entry of nationals from certain Muslim-majority countries, cuts to refugee admissions, and increased scrutiny for visa applicants.

The United States is by far the world's top migration destination, home to roughly one-fifth of all global migrants. In 2016, nearly 44 million immigrants lived in the United States, comprising 13.5 percent of the country's population. Get the most sought-after data available on immigrants and immigration trends, including top countries of origin, legal immigration pathways, enforcement actions, health-care coverage, and much more.

Though small, the population of Canadians in the United States is quite diverse, and includes students, highly skilled professionals on H-1B or NAFTA visas, family migrants, and retirees. Canadian immigrants have much higher educational attainment and incomes than the native- and overall foreign-born populations. This article offers an interesting data snapshot of Canadians in the United States.

High school graduation is a landmark event for students. It also plays an important role in the state accountability systems designed to ensure that schools provide all students a high-quality education. Yet relying on a school's four-year graduation rate for federal accountability purposes can have unintended consequences for English Learners, who may need extra time to graduate.

Faced with a lack of employment opportunities and recurrent poverty, Albanian youth migrate to Italy alone in the hopes of improving their educational prospects or making money for their families. Yet upon arrival, they face many vulnerabilities. While some protections for unaccompanied minors exist in the Italy, the system is greatly fragmented and challenges, including how to return them to Albania, remain persistent.

The Trump administration’s decision to terminate the Deferred Action for Childhood Arrivals (DACA) deportation-relief program launched in 2012 has sparked new urgency to find a longer-term fix for "DREAMers," the unauthorized immigrants brought to the United States as children. This Policy Beat article examines movement in the courts and in Congress on the DREAM Act and similar proposals, exploring likely paths forward.

In its first year, the Trump administration moved to deliver on some of Donald Trump’s campaign promises on immigration, including ramping up enforcement in the U.S. interior and ending the Deferred Action for Childhood Arrivals (DACA) program. The administration also announced the termination of Temporary Protected Status (TPS) for nationals of some countries. This article explores some of the top policy changes.

Approximately 11,500 unaccompanied children were apprehended at the U.S.-Mexico border in May, putting this year on track to exceed 2014's surge. As the U.S. government struggles to care for these child migrants, with public outrage mounting over reports of unsafe, filthy conditions in initial Border Patrol custody, the failure of the executive branch and Congress to plan for increased shelter and care demands are increasingly apparent, as this article explores.

As federal and state governments ramp up efforts to implement the Workforce Innovation and Opportunity Act, these fact sheets compare key characteristics of the foreign born and the U.S. born that are relevant to understanding needs for adult education and workforce training services. The fact sheets cover the United States, the 20 states and 25 counties with the largest immigrant populations, and New York City.

This fact sheet uses U.S. and Mexican apprehensions data to trace the evolving trends in unaccompanied child and family migration from Central America through Mexico and to the United States, and discusses the push factors and pull factors responsible for the increase in flows seen in recent years, as well as the growing role of smuggling organizations.

Growing up with unauthorized immigrant parents puts children—nearly 80 percent of whom were born in the United States—at a disadvantage, with lower preschool enrollment, reduced socioeconomic progress, and higher rates of linguistic isolation and poverty. This fact sheet examines the number, characteristics, and socioeconomic status of children, both U.S.-citizen and noncitizen, who have unauthorized immigrant parents.

A high school diploma has been a core requirement of proposed DREAM Act legislation and the Deferred Action for Childhood Arrivals (DACA) program. Yet a fresh estimate of the number of unauthorized immigrants graduating annually from U.S. high schools has long been missing from the debate. This fact sheet provides up-to-date estimates for the United States and top 15 states, estimating 98,000 such students graduate yearly.

Noncitizens have long served in the U.S. military, often encouraged by the promise of a fast track to U.S. citizenship. In recent years, however, Congress and the Defense Department have made it more difficult for noncitizens to enlist. This brief give context to these policy changes and explores ways the military could better balance concerns about national security and the need for recruits with key cultural and professional skills.

Marking the release of an MPI report, this briefing explores the effects of recent revisions in DHS immigration enforcement priorities on deportations within the U.S. interior.

China has been Africa’s largest trading partner since 2009, and as commerce and investment have increased, so have flows of people in both directions. With an estimated 1 million to 2 million Chinese migrants across Africa, some countries have relaxed their short-term visa requirements in hopes of facilitating cultural and business exchanges. High levels of Chinese investment do not, however, correlate with more liberal visa policies, as this article explores.

This discussion on the 1986 Immigration Reform and Control Act (IRCA) showcases MPI Fellow Charles Kamasaki's book, Immigration Reform: The Corpse That Will Not Die. Kamasaki is joined by other veterans of the IRCA debate for a conversation on the lessons, the intended and unintended consequences, and how the law’s legacy has shaped contemporary politics on immigration.

In the face of an uptick in unauthorized arrivals in Italy from Tunisia in 2017, the European Union dusted off earlier policy proposals such as funding to increase Tunisia’s border-control capabilities and the creation of disembarkation platforms. This article explores why contemporary developments, including a fragile Tunisian political system, suggest the need for a different approach.

While the Global Compact for Safe, Orderly, and Regular Migration was formally adopted by 164 of the UN's 193 Member States, it's worth asking how it became a point of contention and ultimately was rejected by more than a dozen countries. The answer? A long lag time between negotiation and adoption, during which overheated claims against it went largely unanswered, as this commentary explores.

Governments on the receiving end of migrants and refugees reinforced their commitment to returns in 2017, sending or coercing migrants to move back to impoverished or violent homelands. The Dominican Republic pushed out some 70,000 Haitians and native born of Haitian descent, while more than 500,000 Afghans left Iran and Pakistan. Though many of these migrants chose to return, in practice the line between forced and voluntary returns is blurry.