Receptor for hyaluronan-mediated motility (RHAMM) defines an invasive niche associated with tumor progression and predicts poor outcomes in breast cancer patients.

Breast cancer invasion and metastasis result from a complex interplay between tumor cells and the tumor microenvironment (TME). Key oncogenic changes in the TME include aberrant synthesis, processing, and signaling of hyaluronan (HA). Hyaluronan-mediated motility receptor (RHAMM, CD168; HMMR) is an HA receptor enabling tumor cells to sense and respond to this aberrant TME during breast cancer progression. Previous studies have associated RHAMM expression with breast tumor progression; however, cause and effect mechanisms are incompletely established. Focused gene expression analysis of an internal breast cancer patient cohort confirmed that increased RHAMM expression correlates with aggressive clinicopathological features. To probe mechanisms, we developed a novel 27-gene RHAMM-related signature (RRS) by intersecting differentially expressed genes in lymph node (LN)-positive patient cases with the transcriptome of a RHAMM-dependent model of cell transformation, which we validated in an independent cohort. We demonstrate that the RRS predicts for poor survival and is enriched for cell cycle and TME-interaction pathways. Further analyses using CRISPR/Cas9-generated RHAMM-/- breast cancer cells provided direct evidence that RHAMM promotes invasion in vitro and in vivo. Immunohistochemistry studies highlighted heterogeneous RHAMM protein expression, and spatial transcriptomics associated the RRS with RHAMM-high microanatomic foci. We conclude that RHAMM upregulation leads to the formation of 'invasive niches', which are enriched in RRS-related pathways that drive invasion and could be targeted to limit invasive progression and improve patient outcomes. © 2023 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Breast Cancer Collaborative Registry informs understanding of factors predicting sleep quality.

SIGNIFICANCE: Poor sleep quality is a common and persistent problem reported by women with breast cancer (BC). Empirical evidence identifies many risk factors for self-reported sleep deficiency, but inconsistencies limit translation to practice. PURPOSE: To increase understanding of risk factors predicting self-reported poor sleep quality in women with BC who completed the Breast Cancer Collaborative Registry (BCCR) questionnaire. METHODS: This cross-sectional study recruited women with a first diagnosis of BC (n = 1302) at five sites in Nebraska and South Dakota. Women completed the BCCR that includes numerous variables as well as the Pittsburgh Sleep Quality Index (PSQI) and SF36v2 (n = 1260). Descriptive statistics and non-parametric correlations were used to determine associations and create predictive models of sleep quality with BCCR variables and SF36v2 subscales. RESULTS: Most women were white (93.7%) and married (71.5%); mean age was 60.1 (21-90) years. Poor sleep was self-reported by 53% of women. Seven variables were highly associated with sleep quality (p ≤ 0.001). The first model found younger age, lower physical activity, and higher fatigue were the strongest combined and independent variables predicting poor sleep quality (F = 23.0 (p < .001), R2 = 0.103). Participants self-reported lower health status on most SF36v2 subscales [Z = 44.9 (11.6) to 49.1 (10.1)]. A second model found that all subscales were predictors of poor sleep; vitality, mental health, bodily pain, and general health were the strongest predictors (F = 101.3 (p < .001), R2 = 0.26). CONCLUSIONS: Results confirm previously identified risk factors and reveal inconsistencies in other variables. Clinicians need to routinely screen for the identified risk factors of self-reported poor sleep quality.

Two PALB2 germline mutations found in both BRCA1+ and BRCAx familial breast cancer.

Partner and localizer of BRCA2 (PALB2), plays an important functional role in DNA damage repair. Recent studies indicate that germline mutations in PALB2 predispose individuals to a high risk of developing familial breast cancer. Therefore, comprehensive identification of PALB2 germline mutations is potentially important for understanding their roles in tumorigenesis and for testing their potential utility as clinical targets. Most of the previous studies of PALB2 have focused on familial breast cancer cases with normal/wild-type BRCA1 and BRCA2 (BRCAx). We hypothesize that PALB2 genetic mutations also exist in individuals with BRCA mutations (BRCA+). To test this hypothesis, PALB2 germline mutations were screened in 107 exome data sets collected from familial breast cancer families who were either BRCA1+ or BRCAx. Two novel heterozygous mutations predicted to alter the function of PALB2 were identified (c.2014G>C, p.E672Q and c.2993G>A, p.G998E). Notably, both of these mutations co-existed in BRCA1+ and BRCA1x families. These studies show that mutations in PALB2 can occur independent of the status of BRCA1 mutations, and they highlight the importance to include BRCA1+ families in PALB2 mutation screens.

Breast Cancer Risk Reduction, Version 2.2015.

Breast cancer is the most frequently diagnosed malignancy in women in the United States and is second only to lung cancer as a cause of cancer death. To assist women who are at increased risk of developing breast cancer and their physicians in the application of individualized strategies to reduce breast cancer risk, NCCN has developed these guidelines for breast cancer risk reduction.

Family-specific, novel, deleterious germline variants provide a rich resource to identify genetic predispositions for BRCAx familial breast cancer.

BACKGROUND: Genetic predisposition is the primary risk factor for familial breast cancer. For the majority of familial breast cancer, however, the genetic predispositions remain unknown. All newly identified predispositions occur rarely in disease population, and the unknown genetic predispositions are estimated to reach up to total thousands. Family unit is the basic structure of genetics. Because it is an autosomal dominant disease, individuals with a history of familial breast cancer must carry the same genetic predisposition across generations. Therefore, focusing on the cases in lineages of familial breast cancer, rather than pooled cases in disease population, is expected to provide high probability to identify the genetic predisposition for each family. METHODS: In this study, we tested genetic predispositions by analyzing the family-specific variants in familial breast cancer. Using exome sequencing, we analyzed three families and 22 probands with BRCAx (BRCA-negative) familial breast cancer. RESULTS: We observed the presence of family-specific, novel, deleterious germline variants in each family. Of the germline variants identified, many were shared between the disease-affected family members of the same family but not found in different families, which have their own specific variants. Certain variants are putative deleterious genetic predispositions damaging functionally important genes involved in DNA replication and damaging repair, tumor suppression, signal transduction, and phosphorylation. CONCLUSIONS: Our study demonstrates that the predispositions for many BRCAx familial breast cancer families can lie in each disease family. The application of a family-focused approach has the potential to detect many new predispositions.

Genome instability in blood cells of a BRCA1+ breast cancer family.

BACKGROUND: BRCA1 plays an essential role in maintaining genome stability. Inherited BRCA1 germline mutation (BRCA1+) is a determined genetic predisposition leading to high risk of breast cancer. While BRCA1+ induces breast cancer by causing genome instability, most of the knowledge is known about somatic genome instability in breast cancer cells but not germline genome instability. METHODS: Using the exome-sequencing method, we analyzed the genomes of blood cells in a typical BRCA1+ breast cancer family with an exon 13-duplicated founder mutation, including six breast cancer-affected and two breast cancer unaffected members. RESULTS: We identified 23 deleterious mutations in the breast cancer-affected family members, which are absent in the unaffected members. Multiple mutations damaged functionally important and breast cancer-related genes, including transcriptional factor BPTF and FOXP1, ubiquitin ligase CUL4B, phosphorylase kinase PHKG2, and nuclear receptor activator SRA1. Analysis of the mutations between the mothers and daughters shows that most mutations were germline mutation inherited from the ancestor(s) while only a few were somatic mutation generated de novo. CONCLUSION: Our study indicates that BRCA1+ can cause genome instability with both germline and somatic mutations in non-breast cells.

Can unknown predisposition in familial breast cancer be family-specific?

Genetic predisposition plays a key role in the development of familial breast cancer. In spite of strong familial clustering of the disease and extensive efforts made during the past decade; however, progress has been slow in identifying genetic predisposition for the majority of familial breast cancer families. The question arises therefore as to whether current approaches are adequate in identifying the unknown genetic predisposition. We analyzed eight members of a BRCA1-, BRCA2-, p53-, and PTEN-negative breast cancer family, of which five had breast cancer, one is an obligate gene carrier, and two were unaffected. We sequenced the entire coding region of the genome for each member using exome sequencing to identify nonsynonymous variants. We identified 55 nonsynonymous germline variants affecting 49 genes in multiple members of the family, of which 22 are predicted to have damaging effects. We validated 20 of the 22 selected variants in the family by Sanger sequencing. Two variants in KAT6B, an acetal transferase gene, were identified in six family members of which five were affected with breast cancer and one is the unaffected obligate carrier. We further examined the presence of the identified variants in a cohort of 40 additional breast cancer cases from 22 familial breast cancer families, but none of the 22 variants was detected in these cases. Sequencing the entire coding exons in KAT6B detects no variants in these cases. Our results show that genetic predisposition for familial breast cancer can be rich in an affected family, but the predisposition can be family-specific. As such, it will be difficult to detect them by applying population-based approach. Our study supports the concept that focusing on each affected family will be required to determine the genetic predisposition for many familial breast cancer families whose genetic dispositions remain unknown.

BRCA1 regulates the G2/M checkpoint by activating Chk1 kinase upon DNA damage.

The breast cancer tumor-suppressor gene, BRCA1, encodes a protein with a BRCT domain-a motif that is found in many proteins that are implicated in DNA damage response and in genome stability. Phosphorylation of BRCA1 by the DNA damage-response proteins ATM, ATR and hCds1/Chk2 changes in response to DNA damage and at replication-block checkpoints. Although cells that lack BRCA1 have an abnormal response to DNA damage, the exact role of BRCA1 in this process has remained unclear. Here we show that BRCA1 is essential for activating the Chk1 kinase that regulates DNA damage-induced G2/M arrest. Thus, BRCA1 controls the expression, phosphorylation and cellular localization of Cdc25C and Cdc2/cyclin B kinase-proteins that are crucial for the G2/M transition. We show that BRCA1 regulates the expression of both Wee1 kinase, an inhibitor of Cdc2/cyclin B kinase, and the 14-3-3 family of proteins that sequesters phosphorylated Cdc25C and Cdc2/cyclin B kinase in the cytoplasm. We conclude that BRCA1 regulates key effectors that control the G2/M checkpoint and is therefore involved in regulating the onset of mitosis.

Correction: ERK1/2 Signaling Plays an Important Role in Topoisomerase II Poison-Induced G2/M Checkpoint Activation.

[This corrects the article DOI: 10.1371/journal.pone.0050281.].

RAC1 GTPase plays an important role in γ-irradiation induced G2/M checkpoint activation.

INTRODUCTION: In response to gamma-irradiation (IR)-induced double-strand DNA breaks, cells undergo cell-cycle arrest, allowing time for DNA repair before reentering the cell cycle. G2/M checkpoint activation involves activation of ataxia telangiectasia mutated (ATM)/ATM- and rad3-related (ATR) kinases and inhibition of Cdc25 phosphatases, resulting in inhibition of Cdc2 kinase and subsequent G2/M cell-cycle arrest. Previous studies from our laboratory showed that the G2/M checkpoint activation after IR exposure of MCF-7 breast cancer cells is dependent on the activation of extracellular signal-regulated protein kinase 1 and 2 (ERK1/2) signaling. In the present studies, we investigated the role of Ras-related C3 botulinum toxin substrate 1 (Rac1) guanosine triphosphatase (GTPase) in IR-induced G2/M checkpoint response and ERK1/2 activation, as well as in cell survival after IR. METHODS: With Rac1-specific inhibitor, dominant negative mutant Rac1 (N17Rac1) and specific small interfering RNA, the effect of Rac1 on IR-induced G2/M checkpoint response and ERK1/2 activation was examined in human breast cancer cells. In addition, the effect of Rac1 on cell survival after irradiation was assessed by using Rac1-specific inhibitor. RESULTS: IR exposure of MCF-7 breast cancer cells was associated with a marked activation of Rac1 GTPase. Furthermore, inhibition of Rac1 by using specific inhibitor, dominant-negative Rac1 mutant, or specific siRNA resulted in attenuation of IR-induced G2/M arrest and concomitant diminution of IR-induced activation of ATM, ATR, Chk1, and Chk2 kinases, as well as phosphorylation of Cdc2-Tyr15. Moreover, Rac1 inhibition or decreased Rac1 expression also abrogated IR-induced phosphorylation of mitogen-activated protein kinase kinase 1 and 2 (MEK1/2) and ERK1/2. Ultimately, inhibition of Rac1 markedly increased cellular sensitivity to IR exposure, which involves induction of apoptosis. CONCLUSION: Studies in this report suggest that Rac1 GTPase plays an essential role in the activation of IR-induced ERK1/2 signaling and subsequent G2/M checkpoint response. Furthermore, results also support a role for Rac1 in promoting cell survival after irradiation treatment.

Distinct Neoadjuvant Chemotherapy Response and 5-Year Outcome in Patients With Estrogen Receptor-Positive, Human Epidermal Growth Factor Receptor 2-Negative Breast Tumors That Reclassify as Basal-Type by the 80-Gene Signature.

PURPOSE: The 80-gene molecular subtyping signature (80-GS) reclassifies a proportion of immunohistochemistry (IHC)-defined luminal breast cancers (estrogen receptor-positive [ER+], human epidermal growth factor receptor 2-negative [HER2-]) as Basal-Type. We report the association of 80-GS reclassification with neoadjuvant treatment response and 5-year outcome in patients with breast cancer. METHODS: Neoadjuvant Breast Registry Symphony Trial (NBRST; NCT01479101) is an observational, prospective study that included 1,069 patients with early-stage breast cancer age 18-90 years who received neoadjuvant therapy. Pathologic complete response (pCR) and 5-year distant metastasis-free survival (DMFS) and overall survival (OS) were assessed in 477 patients with IHC-defined ER+, HER2- tumors and in a reference group of 229 patients with IHC-defined triple-negative breast cancer (TNBC). RESULTS: 80-GS reclassified 15% of ER+, HER2- tumors (n = 73) as Basal-Type (ER+/Basal), which had similar pCR compared with TNBC/Basal tumors (34% v 38%; P = .52), and significantly higher pCR than ER+/Luminal A (2%; P < .001) and ER+/Luminal B (6%; P < .001) tumors. The 5-year DMFS (%, [95% CI]) was significantly lower for patients with ER+/Basal tumors (66% [52.6 to 77.3]), compared with those with ER+/Luminal A tumors (92.3% [85.2 to 96.1]) and ER+/Luminal B tumors (73.5% [44.5 to 79.3]). Importantly, patients with ER+/Basal or TNBC/Basal tumors that had a pCR exhibited significantly improved DMFS and OS compared with those with residual disease. By contrast, patients with ER+/Luminal B tumors had comparable 5-year DMFS and OS whether or not they achieved pCR. CONCLUSION: Significant differences in chemosensitivity and 5-year outcome suggest patients with ER+/Basal molecular subtype may benefit from neoadjuvant regimens optimized for patients with TNBC/Basal tumors compared with patients with ER+/Luminal subtype. These data highlight the importance of identifying this subset of patients to improve treatment planning and long-term survival.

Correction: Inhibition of RAC1 GTPase sensitizes pancreatic cancer cells to γ-irradiation.

[This corrects the article DOI: 10.18632/oncotarget.2500.].

Heregulin-dependent delay in mitotic progression requires HER4 and BRCA1.

HER4 expression in human breast cancers correlates with a positive prognosis. While heregulin inhibits the growth of HER4-positive breast cancer cells, it does so by undefined mechanisms. We demonstrate that heregulin-induced HER4 activity inhibits cell proliferation and delays G(2)/M progression of breast cancer cells. While investigating pathways of G(2)/M delay, we noted that heregulin increased the expression of BRCA1 in a HER4-dependent, HER2-independent manner. Induction of BRCA1 by HER4 occurred independently of the cell cycle. Moreover, BRCA1 expression was elevated in HER4-postive human breast cancer specimens. Heregulin stimulated c-Jun N-terminal kinase (JNK), and pharmacologic inhibition of JNK impaired heregulin-enhanced expression of BRCA1 and mitotic delay; inhibition of Erk1/2 did not. Knockdown of BRCA1 with small interfering RNA in a human breast cancer cell line interfered with HER4-mediated mitotic delay. Heregulin/HER4-dependent mitotic delay was examined further with an isogenic pair of mouse mammary epithelial cells (MECs) derived from mice harboring homozygous LoxP sites flanking exon 11 of BRCA1, such that one cell line expressed BRCA1 while the other cell line, after Cre-mediated excision, did not. BRCA1-positive MECs displayed heregulin-dependent mitotic delay; however, the isogenic BRCA1-negative MECs did not. These results suggest that heregulin-mediated growth inhibition in HER4-postive breast cancer cells requires BRCA1.

Telomeric DNA induces apoptosis and senescence of human breast carcinoma cells.

INTRODUCTION: Cancer is a leading cause of death in Americans. We have identified an inducible cancer avoidance mechanism in cells that reduces mutation rate, reduces and delays carcinogenesis after carcinogen exposure, and induces apoptosis and/or senescence of already transformed cells by simultaneously activating multiple overlapping and redundant DNA damage response pathways. METHODS: The human breast carcinoma cell line MCF-7, the adriamycin-resistant MCF-7 (Adr/MCF-7) cell line, as well as normal human mammary epithelial (NME) cells were treated with DNA oligonucleotides homologous to the telomere 3' overhang (T-oligos). SCID mice received intravenous injections of MCF-7 cells followed by intravenous administration of T-oligos. RESULTS: Acting through ataxia telangiectasia mutated (ATM) and its downstream effectors, T-oligos induced apoptosis and senescence of MCF-7 cells but not NME cells, in which these signaling pathways were induced to a far lesser extent. In MCF-7 cells, experimental telomere loop disruption caused identical responses, consistent with the hypothesis that T-oligos act by mimicking telomere overhang exposure. In vivo, T-oligos greatly prolonged survival of SCID mice following intravenous injection of human breast carcinoma cells. CONCLUSION: By inducing DNA damage-like responses in MCF-7 cells, T-oligos provide insight into innate cancer avoidance mechanisms and may offer a novel approach to treatment of breast cancer and other malignancies.

Expression of kinase suppressor of Ras1 enhances cisplatin-induced extracellular signal-regulated kinase activation and cisplatin sensitivity.

Kinase suppressor of Ras1 (KSR1) interacts with several mitogen-activated protein (MAP) kinase pathway components, including Raf, MAP/extracellular signal-regulated kinase (ERK) kinase (MEK), and ERK, and acts as a positive regulator of the Ras signaling cascade. Previous studies have shown that exposure of cells to the anticancer agent cisplatin (cis-diamminedichloroplatinum, CDDP) is associated with changes in multiple signal transduction pathways, including c-Jun-NH2-kinase, ERK, and p38 pathways. Moreover, ERK activation has been linked to changes in cell survival following CDDP treatment. In this report, we have examined the effects of KSR1 expression on the sensitivity of cells to CDDP-induced apoptosis. Loss of KSR1 expression in mouse embryo fibroblasts (MEFs) derived from KSR1 knockout mice (KSR-/- MEF) is associated with decreased CDDP-induced ERK activation and increased resistance to CDDP-induced apoptosis compared with wild-type MEFs (KSR+/+ MEF). Furthermore, transduction of KSR-/- MEFs and MCF-7 breast cancer cells with wild-type KSR1 resulted in enhanced ERK activation following CDDP exposure and increased sensitivity to CDDP. In addition, inhibition of ERK activation by exposing MEFs to the MEK1/2-specific inhibitors PD98059 and U0126 protected both KSR+/+ and KSR-/- MEFs cells from CDDP-induced apoptosis. These results indicate that KSR1-mediated regulation of ERK activity represents a novel determinant of CDDP sensitivity of cancer cells.

BRCA1-mediated G2/M cell cycle arrest requires ERK1/2 kinase activation.

Germline mutations in the BRCA1 gene are associated with an increased susceptibility to the development of breast and ovarian cancers. Evidence suggests that BRCA1 protein plays a key role in mediating DNA damage-induced checkpoint responses. Several studies have shown that ectopic expression of BRCA1 in human cells can trigger cellular responses similar to those induced by DNA damage, including G2/M cell cycle arrest and apoptosis. While the effects of ectopic BRCA1 expression on the G2/M transition and apoptosis have been extensively studied, the factors that dictate the balance between these two responses remain poorly understood. We have recently shown that ectopic expression of BRCA1 in MCF-7 human breast cancer cells resulted in activation of extracellular signal-regulated protein kinase 1 and 2 (ERK1/2) and G2/M cell cycle arrest. Furthermore, inhibition of BRCA1-induced ERK1/2 activation using mitogen-activated protein kinase kinase 1 and 2 (MEK1/2)-specific inhibitors resulted in increased apoptosis, suggesting a potential role of ERK1/2 kinases in BRCA1-mediated G2/M checkpoint response. In this study, we assessed the role of ERK1/2 kinases in the regulation of BRCA1-mediated G2/M cell cycle arrest. Results indicate that BRCA1-induced G2/M cell cycle arrest and ERK1/2 activation correlate with changes in the level and/or activity of several key regulators of the G2/M checkpoint, including activation of Chk1 and Wee1 kinases, induction of 14-3-3, and down-regulation of Cdc25C. Furthermore, inhibition of ERK1/2 kinases using MEK1/2-specific inhibitors results in a marked attenuation of the BRCA1-induced G2/M arrest. Biochemical studies established that ERK1/2 inhibition abolished the effects of BRCA1 on components of the G2/M checkpoint, including regulation of Cdc25C expression and activation of Wee1 and Chk1 kinases. These results implicate a critical role of ERK1/2 signaling in the regulation of BRCA1 function on controlling the G2/M checkpoint responses.

Exome analysis reveals differentially mutated gene signatures of stage, grade and subtype in breast cancers.

Breast cancers exhibit highly heterogeneous molecular profiles. Although gene expression profiles have been used to predict the risks and prognostic outcomes of breast cancers, the high variability of gene expression limits its clinical application. In contrast, genetic mutation profiles would be more advantageous than gene expression profiles because genetic mutations can be stably detected and the mutational heterogeneity widely exists in breast cancer genomes. We analyzed 98 breast cancer whole exome samples that were sorted into three subtypes, two grades and two stages. The sum deleterious effect of all mutations in each gene was scored to identify differentially mutated genes (DMGs) for this case-control study. DMGs were corroborated using extensive published knowledge. Functional consequences of deleterious SNVs on protein structure and function were also investigated. Genes such as ERBB2, ESP8, PPP2R4, KIAA0922, SP4, CENPJ, PRCP and SELP that have been experimentally or clinically verified to be tightly associated with breast cancer prognosis are among the DMGs identified in this study. We also identified some genes such as ARL6IP5, RAET1E, and ANO7 that could be crucial for breast cancer development and prognosis. Further, SNVs such as rs1058808, rs2480452, rs61751507, rs79167802, rs11540666, and rs2229437 that potentially influence protein functions are observed at significantly different frequencies in different comparison groups. Protein structure modeling revealed that many non-synonymous SNVs have a deleterious effect on protein stability, structure and function. Mutational profiling at gene- and SNV-level revealed differential patterns within each breast cancer comparison group, and the gene signatures correlate with expected prognostic characteristics of breast cancer classes. Some of the genes and SNVs identified in this study show high promise and are worthy of further investigation by experimental studies.

Adenovirus expressing p27KIP1 induces apoptosis against cholangiocarcinoma cells by triggering Fas ligand on the cell surface.

BACKGROUND/AIMS: The prognosis of patients with cholangiocarcinoma is poor because of the difficulty of surgical curative resection. Therefore, other effective treatments must be developed especially those involving gene therapy. p27kip1, one of the cyclin-dependent kinase inhibitors, is known to limit proliferation of the cells. Our previous reports have shown that the overexpression of p27kip1 by a recombinant adenoviral vector expressing p27kip1 (Adp27) induces apoptosis. However, the mechanism of the Adp27-mediated apoptosis is not still resolved. Activation of the Fas pathway is one of the important gates for apoptosis. In this report, we examined whether p27kip1-induced apoptosis is closely related to the Fas/Fas ligand (FasL) system. RESULTS: After infection of Adp27, flow cytometric analysis showed that Fas ligand was expressed on the cell surface of cholangiocarcinoma cell lines (TFK-1). In spite of detecting the cell surface expression of Fas ligand, overexpression of p27kip1 increased no amount of Fas ligand in mRNA by quantitative RT-PCR and protein level by Western blot. In addition, the immunocytochemical analysis showed that Fas ligand was adequately stored within the cytosol of TFK-1 cells. More interestingly, Adp27-induced apoptosis was completely inhibited by the neutralizing antibody of Fas ligand (NOK-1). This result suggests that overexpression of p27kip1 may deliver Fas ligand to the cell surface and mainly utilizes the Fas pathway as a gate of apoptosis. CONCLUSIONS: This is the first report to prove that Adp27-mediated apoptosis utilizes the Fas pathway by delivering Fas ligand to the cell surface.