SUMMARY Breast cancer suppressor BRCA2 is critical for maintenance of genomic integrity and resistance to agents that damage DNA or collapse replication forks, presumably through homology-directed repair of double-strand breaks (HDR). Using single-molecule DNA fiber analysis, we show here that nascent replication tracts created before fork stalling with hydroxyurea are degraded in the absence of BRCA2 but are stable in wild-type cells. BRCA2 mutational analysis reveals that a conserved C-terminal site, involved in stabilizing RAD51 filaments but not in loading RAD51 onto DNA, is essential for this fork protection but dispensable for HDR. RAD51 filament disruption in wild-type cells phenocopies BRCA2 deficiency. BRCA2 prevents chromosomal aberrations upon replication stalling, which are alleviated by inhibition of MRE11, the nuclease responsible for this novel fork instability. Thus, BRCA2 prevents rather than repairs nucleolytic lesions at stalled replication forks to maintain genomic integrity, and hence likely suppresses tumorigenesis through this novel replication-specific function.

SUMMARY Genes mutated in patients with Fanconi anemia (FA) interact with the DNA repair genes BRCA1 and BRCA2/FANCD1 to suppress tumorigenesis, but the molecular functions ascribed to them cannot fully explain all of their cellular roles. Here, we show a repair-independent requirement for FA genes, including FANCD2, and BRCA1 in protecting stalled replication forks from degradation. Fork protection is surprisingly rescued in FANCD2-deficient cells by elevated RAD51 levels or stabilized RAD51 filaments. Moreover, FANCD2-mediated fork protection is epistatic with RAD51 functions, revealing an unanticipated fork protection pathway that connects FA genes to RAD51 and the BRCA1/2 breast cancer suppressors. Collective results imply a unified molecular mechanism for repair-independent functions of FA, RAD51, and BRCA1/2 proteins in preventing genomic instability and suppressing tumorigenesis.

Exhausted T cells in chronic infections and cancer have sustained expression of the inhibitory receptor programmed cell death 1 (PD-1). Therapies that block the PD-1 pathway have shown promising clinical results in a significant number of advanced-stage cancer patients. Nonetheless, a better understanding of the immunological responses induced by PD-1 blockade in cancer patients is lacking. Identification of predictive biomarkers is a priority in the field, but whether peripheral blood analysis can provide biomarkers to monitor or predict patients’ responses to treatment remains to be resolved. In this study, we analyzed longitudinal blood samples from advanced stage non–small cell lung cancer (NSCLC) patients (n = 29) receiving PD-1–targeted therapies. We detected an increase in Ki-67+ PD-1+ CD8 T cells following therapy in ∼70% of patients, and most responses were induced after the first or second treatment cycle. This T-cell activation was not indiscriminate because we observed only minimal effects on EBV-specific CD8 T cells, suggesting that responding cells may be tumor specific. These proliferating CD8 T cells had an effector-like phenotype (HLA-DR+, CD38+, Bcl-2lo), expressed costimulatory molecules (CD28, CD27, ICOS), and had high levels of PD-1 and coexpression of CTLA-4. We found that 70% of patients with disease progression had either a delayed or absent PD-1+ CD8 T-cell response, whereas 80% of patients with clinical benefit exhibited PD-1+ CD8 T-cell responses within 4 wk of treatment initiation. Our results suggest that peripheral blood analysis may provide valuable insights into NSCLC patients’ responses to PD-1–targeted therapies.

Importance Four assays have been registered with the FDA to detect PD-L1 to enrich for patient response to anti-PD-1/PD-L1 therapies. The tests use four separate PD-L1 antibodies on two separate staining platforms and have their own scoring systems which raises questions about their similarity and potential cross-utilization. Objective We compared the performance of four PD-L1 platforms, including two FDA-cleared assays and two laboratory developed tests (LDTs). Design Four serial histology sections from 90 archival NSCLCs were distributed to three sites that performed the following IHCs: 1) 28-8 antibody on Dako Link 48; 2) 22c3 antibody on Dako Link 48; 3) SP142 antibody on Ventana Benchmark; and 4) E1L3N antibody on Leica Bond. Slides were scanned and scored by thirteen pathologists by estimating the percentage of malignant and immune cells expressing PD-L1. Intraclass correlation coefficients (ICC) and paired and mixed effects statistical analyses were performed to compare antibodies and pathologists scoring of tumor and immune cells. Results The SP142 Ventana assay was an outlier with a significantly lower mean score of PD-L1 expression in both tumor and immune cells. Pairwise comparisons showed the 28-8 and E1L3N were not significantly different, but that 22c3 showed a slight but statistically significant reduction in tumor cell labeling. Evaluation of ICC between antibodies to quantify inter-assay variability using the average of thirteen pathologists scores for tumor shows very high concordance between antibodies for tumor cell scoring (0.813) and lower levels of concordance for immune cell scoring (0.277). When examining inter-pathologists variability for any single antibody, the concordance between pathologists’ reads for tumor ranged from ICC of 0.83 to 0.88 for each antibody while the ICC from immune cells for each antibody ranged from 0.17 to 0.23. Conclusions The assay using the SP142 antibody is a clear outlier detecting significantly less tumor cell and immune cell PD-L1 expression. Antibody 22c3 shows slight yet statistically significantly lower staining than either 28-8 or E1L3N, but this significance is only detected when using the average of thirteen pathologist scores. Pathologists show excellent concordance when scoring tumor cells stained with any antibody, but poor concordance for scoring immune cell staining.

Abstract. Two relatexl cellular proteins, p80 and p85 (cortactin), become phosphorylated on tyrosine in pp60"~-transformed cells and in cells stimulated with certain growth factors. The amino-terminal half of cortactin is comprised of multiple copies of an internal, tandem 37-amino acid repeat. The carboxylterminal half contains a distal SH3 domain. We report that cortactin is an F-actin-binding protein. The binding to F-actin is specific and saturable. The aminoterminal repeat region appears to be both necessary and sufficient to mediate actin binding, whereas the SH3 domain had no apparent effect on the actinbinding activity. Cortactin, present in several different cell types, is enriched in cortical structures such as membrane ruffles and lamellipodia. The properties of cortactin indicate that it may be important for microfilament-membrane interactions as well as transducing signals from the cell surface to the cytoskeleton. We suggest the name cortactin, reflecting the cortical subcellular localization and its actin-binding activity.

Transformation of cells by the src oncogene results in elevated tyrosine phosphorylation of two related proteins, p80 and p85 (p80/85). Immunostaining with specific monoclonal antibodies revealed a striking change of subcellular localization of p80/85 in src-transformed cells. p80/85 colocalizes with F-actin in peripheral extensions of normal cells and rosettes (podosomes) of src-transformed cells. Sequence analysis of cDNA clones encoding p80/85 revealed an amino-terminal domain composed of six copies of a direct tandem repeat, each repeat containing 37 amino acids, a carboxyl-terminal SH3 domain, and an interdomain region composed of a highly charged acidic region and a region rich in proline, serine, and threonine. The multidomain structure of p80/85 and its colocalization with F-actin in normal and src-transformed cells suggest that these proteins may associate with components of the cytoskeleton and contribute to organization of cell structure.Transformation of cells by tyrosine kinase oncogenes leads to alterations of cell shape, cellular metabolism, growth control, and gene expression (16,31,54). A substantial body of evidence indicates that many if not all of these changes are a direct result of the tyrosine kinase activity of the oncogene product (reviewed in references 31, 54, and 66). Rous sarcoma virus (RSV) encodes an enzymatically activated, 60-kDa tyrosine protein kinase, pp60v"src (6,15,44). However, the product of the normal cellular homolog of src, pp60c-sc, is enzymatically down regulated and does not induce significant alterations in cellular growth or changes in cell morphology when overexpressed in rodent or avian cells (30,53,67). Oncogenic activation of c-src and concomitant activation of tyrosine kinase activity can be achieved by mutation of the regulatory site of tyrosine phosphorylation, 40,58,63). Thus, expression of pp6Ov-src or activated forms of the c-src protein pp60527F results in efficient cellular transformation and the increased tyrosine phosphorylation of approximately 15 to 30 cellular proteins (27,33,45,61).Genetic studies have shown that structural perturbation of several different domains of pp6Osrc leads to alterations in the pattern of tyrosine phosphorylation of specific cellular proteins and accompanying changes in morphological phenotypes (reviewed in references 31 and 54). For example, mutation of the site of myristylation (e.g., Gly-2 to Ala) of pp60v-src or pp60527F blocks cellular transformation (9, 32, 61) and the tyrosine phosphorylation of a 120-kDa cellular protein (35,45,61). pp60src contains two regions that share amino acid sequence similarity with other nonreceptor tyrosine protein kinases (55) and regulatory proteins such as phospholipase C--y, Crk, and GTPase-activating protein (GAP) (70,73,76). Structural alterations within these regions alter or abolish the transforming activity of src (18,28,51,59,77,79) Whereas recent experiments have shown that tyrosine phosphorylation of some cellular proteins appears to direct stable protein-protein interactio...

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Senescent cells extrude fragments of chromatin from the nucleus into the cytoplasm, where they are processed by an autophagic/lysosomal pathway.