Retinoblastoma Susceptibility Gene Research Articles

RB1 genetic alterations in estrogen receptor-positive breast carcinomas: Correlation with neuroendocrine differentiation

Genetic alterations in the retinoblastoma susceptibility gene (RB1) are present in up to 40% of triple-negative breast cancers (BCs) and frequent in tumors with neuroendocrine differentiation, including small cell neuroendocrine carcinoma. Data on RB1 genetic alterations in estrogen receptor (ER)-positive BCs is scarce. In this study, we sought to define the morphologic, immunohistochemical and genetic features of ER-positive BCs harboring somatic alterations in RB1, with emphasis on neuroendocrine differentiation. ER-positive BCs with pathogenic RB1 genetic alterations were identified in less than 1% of cases from a cohort of 6,026 BCs previously subjected to targeted next-generation sequencing, including 23 primary BCs (pBCs) and 32 recurrent/metastatic BCs (mBCs). In cases where loss of heterozygosity (LOH) of the wild type RB1 allele could be assessed (93%, 51/55), most pBCs (82%, 18/22) and mBCs (90%, 26/29) exhibited biallelic RB1 inactivation, primarily through loss-of-function mutation and LOH (98%, 43/44). Upon histologic review, a subset of RB1-altered tumors exhibited neuroendocrine morphology (13%, 7/55), which correlated with expression of neuroendocrine markers (39%, 9/23) in both pBC (27%, 3/11) and mBCs (50%, 6/12). Loss of Rb protein expression was observed in BCs with biallelic RB1 loss only, with similar frequency in pBCs (82%, 9/11) and mBCs (75%, 9/12). All cases with neuroendocrine marker expression (n=9) and/or neuroendocrine morphology (n=7) harbored biallelic genetic inactivation of RB1 and exhibited Rb loss of expression. TP53 (53%, 29/55) and PIK3CA (45%, 25/55) were the most frequently co-mutated genes across the cohort. Overall, these findings suggest that ER-positive BCs with biallelic RB1 genetic alterations frequently exhibit Rb protein loss, which correlates with neuroendocrine differentiation in select BCs. This study provides insights into the molecular and phenotypic heterogeneity of BCs with RB1 genetic inactivation, underscoring the need for further research into the potential clinical implications associated with these tumors.

Risk of Second Tumors in Retinoblastoma Survivors after Ionizing Radiation: A Review.

Retinoblastoma (RB) is the most common ocular neoplasm in children, whose development depends on two mutational events that occur in both alleles of the retinoblastoma susceptibility gene (RB1). Regarding the nature of these mutational events, RB can be classified as hereditary if the first event is a germline mutation and the second one is a somatic mutation in retina cells or nonhereditary if both mutational events occur in somatic cells. Although the rate of survival of RB is significantly elevated, the incidence of second malignant neoplasms (SMNs) is a concern, since SMNs are the main cause of death in these patients. Effectively, RB patients present a higher risk of SMN incidence compared to other oncology patients. Furthermore, evidence confirms that hereditary RB survivors are at a higher risk for SMNs than nonhereditary RB survivors. Over the decades, some studies have been performed to better understand this subject, evaluating the risk of the development of SMNs in RB patients. Furthermore, this risk seems to increase with the use of ionizing radiation in some therapeutic approaches commonly used in the treatment of RB. This review aims to clarify the effect of ionizing radiation in RB patients and to understand the association between the risk of SMN incidence in patients that underwent radiation therapy, especially in hereditary RB individuals.

Landscape of RB1 alterations in 22,432 Chinese solid tumor patients.

BackgroundThe human retinoblastoma susceptibility gene (RB1) is a tumor-suppressor gene mutated at different frequencies in many different cancers. The aim of the present study was to investigate the distribution of overall RB1 mutation and different mutation types in a range of Chinese patients with solid tumors.MethodsWe investigated RB1 mutations in formalin-fixed, paraffin-embedded (FFPE) tissues of cancer patients who underwent next-generation sequencing (NGS) at 3DMed Clinical Laboratory Inc from January 1, 2017 to April 15, 2020.ResultsGenomic alterations in RB1 were identified in 1,712 (7.6%) of 22,432 patients with more than 20 different cancer entities (58% males and 42% females, median age: 60 years). RB1 mutations occurred most frequently in small-cell lung cancer (SCLC; 138/165, 83.6%), followed by neuroendocrine neoplasms (40/170, 23.5%), bladder cancer (40/209, 19.1%), hepatocellular carcinoma (233/1,649, 14.1%), sarcomas (71/554, 12.8%), and esophageal cancer (32/293, 10.9%). Of these 1,712 patients, 185 (10.8%) had germline RB1 mutations. When stratified by mutational type, 1,258 (5.6%) had single-nucleotide variants (SNVs), 59 (0.3%) had fusions, and 210 (0.9%) had RB1 loss.ConclusionsOur findings indicate that RB1 alterations are widely distributed in solid cancers of many different histotypes in China, with specific mutations differing largely among different tumor types. The present study provides a comprehensive landscape of RB1 mutations in Chinese solid tumor patient and suggests a novel therapeutic target for cancer treatment.

Retinoblastoma Protein Paralogs and Tumor Suppression.

The retinoblastoma susceptibility gene (RB1) is the first tumor suppressor gene discovered and a prototype for understanding regulatory networks that function in opposition to oncogenic stimuli. More than 3 decades of research has firmly established a widespread and prominent role for RB1 in human cancer. Yet, this gene encodes but one of three structurally and functionally related proteins that comprise the pocket protein family. A central question in the field is whether the additional genes in this family, RBL1 and RBL2, are important tumor suppressor genes. If so, how does their tumor suppressor activity overlap or differ from RB1. Here we revisit these questions by reviewing relevant data from human cancer genome sequencing studies that have been rapidly accumulating in recent years as well as pertinent functional studies in genetically engineered mice. We conclude that RBL1 and RBL2 do have important tumor suppressor activity in some contexts, but RB1 remains the dominant tumor suppressor in the family. Given their similarities, we speculate on why RB1 tumor suppressor activity is unique.

Abstract 2229: Landscape of RB1 alterations in 22,432 Chinese solid tumor patients

Abstract Background: The retinoblastoma susceptibility gene (RB1) is one of tumor suppressor genes. This gene is mutated at variable frequencies in a variety of other human cancers. Cancer genome sequencing revealed that most types of cancer with RB1 mutation were retinoblastomas, osteosarcomas, and small-cell lung cancers, and its mutation was also found in other cancer types with a lower frequency, for instance, prostate cancer, breast cancer and etc. RB1 protein plays a prominent role in a variety of molecular processes related to DNA including gene transcription, DNA replication, DNA repair, and mitosis. However, no comprehensive status of RB1 alterations in Chinese populations with solid tumor has been reported yet. Methods: The Formalin-Fixed Paraffin-Embedded (FFPE) tissues from solid tumor patients who have underwent next-generation sequencing (NGS) from January 01, 2017 to April 15, 2020 in 3DMed Clinical Laboratory Inc. (a College of American Pathologists (CAP) and Clinical Laboratory Improvement Amendments (CLIA) certified laboratory) were analyzed. The diagnosis of the tissues was confirmed by hematoxylin and eosin (H&E) staining. The single nucleotide variants (SNVs), copy number variants (CNVs) and gene rearrangements data of these patients were analyzed. Results: Of 22,432 Chinese solid tumor patients with more than 20 tumor types (58% males and 42% females, with median age was 60 years), genomic alterations in RB1 were observed in 1712 (7.6%) patients. RB1 mutations occurred most frequently in small cell lung cancer (138/165, 83.6%), followed by neuroendocrine neoplasms (42/170, 24.7%), sarcoma (127/554, 22.9%), biliary tract cancer (40/209, 19.1%), head and neck cancer (4/22, 18.2%), and liver cancer (232/1649, 14.1%). And (185/1712, 10.8%) patients were detected with germline RB1 mutation. When stratified by the mutational types, 1,443 (6.4%) patients were with SNVs, 59 (0.3%) with fusions, and 210 (0.9%) with loss in RB1 gene. Conclusion: Our results suggested RB1 alteration was widely occurred in solid tumor patients in China, and specific alteration rates differed largely between tumor types. Our study also suggested usage of NGS in the need for individualized characterization of cancers and further investigations are warranted for the cancer treatment upon molecular profiling in the clinical therapeutic setting. Citation Format: Nan Wang, Xueke She, Depei Huang, Xudong Shen, Hushan Zhang, Gang Ji. Landscape of RB1 alterations in 22,432 Chinese solid tumor patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2229.

Impact of RB1 gene mutation type in retinoblastoma patients on clinical presentation and management outcome

Objective/backgroundRetinoblastoma (RB), the most common intraocular malignancy in children, is caused by biallelic inactivation of the human retinoblastoma susceptibility gene (RB1). We are evaluating the impact of the type of RB1 gene mutation on clinical presentation and management outcome. MethodsA retrospective case series of 50 patients with RB. Main outcomes were clinical and pathologic features and types of RB1 gene mutations detected using quantitative multiplex polymerase chain reaction (PCR), allele-specific PCR, next-generation sequencing analysis, and Sanger sequencing. ResultsTwenty (40%) patients had unilateral RB and 30 (60%) had bilateral RB. Overall, 36 (72%) patients had germline disease, 17 (47%) of whom inherited the disease. Of these 17 inherited cases, paternal origin of the RB1 mutation was seen in 15 (88%). The overall eye salvage rate was 74% (n = 49/66; 100% for Groups A + B + C, and 79% for Group D eyes). The most frequent type of mutation was a nonsense mutation generating a stop codon (15/36, 42%). Other mutations that result in a premature stop codon due to deletions or insertions with donor splice site or receptor splice site mutations were detected in 7/36 (19%), 10/36 (28%), and 2/26 (6%) patients, respectively. The remaining two (6%) patients had frameshift mutation. Patients with deletion, acceptor splice site, and frameshift mutations presented with more advanced ICRB (International Classification of Retinoblastoma) stage (75% diagnosed with Group D or E), even though there was no significant difference in eye salvage rate or tumor invasiveness between patients with different types of mutations. ConclusionDespite the heterogeneous nature of RB1 gene mutations, tumor stage remains the most important predictive factor for clinical presentation and outcome. Furthermore, acceptor splice site and frameshift mutations are associated with more advanced tumor stage at diagnosis.

Cytogenetic abnormalities in patients with newly diagnosed multiple myeloma as a secondary primary malignancy: a retrospective study

ABSTRACT Objectives: Multiple myeloma (MM) often develops as a secondary primary malignancy (SPM). The retinoblastoma susceptibility gene (RB1) was the first tumour suppressor gene to be identified. We pooled and analyzed available data to compare the incidence of RB1 gene deletions and other cytogenetic abnormalities in patients with MM alone or as an SPM. Methods: We conducted a retrospective study of 475 patients. The experimental group comprised 18 patients with MM as an SPM, and the control group comprised 457 MM patients. We analyzed the baseline information in both groups, and used the odds ratio (OR), 95% confidence interval (CI), and forest plot to determine the incidence of SPMs with and without cytogenetic abnormalities. Results: The incidence of RB1 gene deletion was higher in the experimental group. There was no significant difference in other cytogenetic abnormalities. Conclusions: RB1 gene deletions appear to be associated with MM that develops as an SPM.

Absence of Pathogenicity in Non-Human Primates of Mutations Related to Retinoblastoma in Humans

The tumor suppressor, Human Retinoblastoma Susceptibility Gene (RB1) plays a prominent role in normal development, gene transcription, DNA replication, repair, and mitosis, and its complete biallelic dysfunction in retinoblasts is the main cause of retinoblastoma in humans. Comparisons between the reference, human RB1 coding region with its counterparts in 19 non-human primates showed that several RB1 alterations accompanying retinoblastoma in the human were present in several non-human primates without apparent pathological effects. Comparative analyses of molecular data were most useful for tracing the evolution of RB1, identifying the polarity of mutational events, the physico-chemical effects conferred by amino acid substitutions, and the number of codons under selection. These historic reconstructions indicated that several RB1 mutations found in retinoblastoma in the human were presumably atavistic, accounting for evolutionary regressions. Moreover, some same-sense RB1 mutations, despite specifying for the same amino acids, were probably ancient adaptations that took place in our evolutionary lineage.

The human retinoblastoma susceptibility gene (RB1): an evolutionary story in primates.

The tumor suppressor gene RB1 (Human Retinoblastoma Susceptibility Gene) plays a prominent role in normal development, gene transcription, DNA replication, repair, and mitosis. Its complete biallelic dysfunction in retinoblasts is the main cause of retinoblastoma in the human. Although this gene has been evolutionary conserved, comparisons between the reference and human RB1 coding region with its counterparts in 19 non-human primates showed 359 sites where nucleotide replacements took place during the radiation of these species. These resulted in missense substitutions in 97 codons, 91 of which by amino acids with radically different physicochemical properties. Several in frame deletions and two insertions were also observed in the N-terminal region of the pRB protein where the highest number of amino acid substitutions and radical amino changes were found. Fifty-six codons were inferred to be under negative selection and five under positive selection. Differences in codon usage showed evident phylogenetic signals, with hominids generally presenting higher indices of codon bias than other catarrhines. The lineage leading to platyrrhines and, within platyrrhines, the lineage leading to Saimiri boliviensis showed a high rate of nucleotide substitutions and amino acids. Finally, several RB1 alterations associated to retinoblastoma in the human were present in several non-human primates without an apparent pathological effect.

RB1: a prototype tumor suppressor and an enigma.

The retinoblastoma susceptibility gene (RB1) was the first tumor suppressor gene to be molecularly defined. RB1 mutations occur in almost all familial and sporadic forms of retinoblastoma, and this gene is mutated at variable frequencies in a variety of other human cancers. Because of its early discovery, the recessive nature of RB1 mutations, and its frequency of inactivation, RB1 is often described as a prototype for the class of tumor suppressor genes. Its gene product (pRB) regulates transcription and is a negative regulator of cell proliferation. Although these general features are well established, a precise description of pRB's mechanism of action has remained elusive. Indeed, in many regards, pRB remains an enigma. This review summarizes some recent developments in pRB research and focuses on progress toward answers for the three fundamental questions that sit at the heart of the pRB literature: What does pRB do? How does the inactivation of RB change the cell? How can our knowledge of RB function be exploited to provide better treatment for cancer patients?

Genetic perspective of retinoblastoma: From present to future.

Retinoblastoma (RB) is the most common malignant intraocular tumor in children. In the last decade, basic research has led to a better understanding of events after two hits in RB susceptibility gene (RB1), molecular mechanism of tumor growth, the cell of origin of RB, etc. This would pave way to identify biomarkers and molecular targeted therapy for better treatment option in the future. Furthermore, improvement in molecular techniques has led to enhanced diagnostic methods for early diagnosis, genetic counseling, and prevention of the disease. This review will help to understand the essence of basic research work conducted in recent times and its implication in the management of RB in the future.

Aberrant cytoplasmic accumulation of retinoblastoma protein in basal cells may lead to increased survival in malignant canine mammary tumours

The retinoblastoma susceptibility gene RB-1 is a tumour suppressor gene that encodes a protein (Rb) that regulates the transition from the G1 phase to the S phase of the cell cycle. Inactivation of the Rb gene has been shown in a variety of human tumours, including breast, ovarian, hepatic, prostatic, and endometrial carcinomas. Although Rb protein is normally expressed in the nuclei of healthy cells, during carcinogenesis there is a partial or complete loss of nuclear expression. Recently, some reports have indicated aberrant cytoplasmic expression of Rb protein. However, little is known about its cytoplasmic expression and significance as a prognostic marker in canine mammary tumours (CMT). The present study was performed on 36 malignant CMT cases in order to assess the mutational status and prognostic significance of Rb in primary malignant CMT. We report an almost complete loss of nuclear expression of Rb protein with corresponding gain of aberrant cytoplasmic expression in basal/myoepithelial cells in CMT. Strikingly, our analysis reveals a significant positive correlation between survival time and cytoplasmic expression of Rb protein in basal cells. Moreover, cytoplasmic expression of Rb protein in basal cells was also correlated with tumour grade and stage.  

TRAP1 is Involved in Cell Cycle Regulated by Retinoblastoma Susceptibility Gene (RB1) in Early Hypoxia and has Variable Expression Patterns in Human Tumors

Tumor necrosis factor receptor associated protein 1(TRAP1) is a member of the Hsp90 family that acts as a molecular chaperon to the tumor suppressor retinoblastoma susceptibility gene (RB1). We have previously demonstrated that TRAP1-positive cells contain a high level of cell proliferating genes, whilst TRAP1-negative cells contain a high level of genes involved in cell cycles and metastases. In this study, we performed a functional analysis of TRAP1 which focused on its regulation within a cell cycle in relation to RB1. Following a heat shock, TRAP1 translocates to the nucleus and chaperonsRB1. When TRAP1 is silenced by siRNA, or prevented from entering the nucleus in hypoxic cells, formation of RB1/E2F1 complexes is impaired and cell cycle activity is promoted by deregulating the G1/S transition. Inhibition of the nuclear translocation of TRAP1 with geldanamycin abrogates its ability to maintain RB1 in a form that associates with E2F1. Restoration of TRAP1 expression reverses these effects. We analysed TRAP1/RB1 expression on 630 tumors by immunohistochemical staining and found TRAP1 lost in some types of cancer, such as non-small cell lung cancer and breast cancer, and the positive correlation of TRAP1 expression in nuclear and cytoplasm with RB1 was observed. Clinico-pathological data showed that breast carcinoma patients lacking nuclear TRAP1 have a shorter disease free survival. Our data suggests that nuclear translocation of TRAP1 is crucial for its function as a chaperon. The loss of TRAP1 expression in certain types of cancer may provide the growth advantage due to the lost control at cell cycle check point.

Tumor suppressor genes associated with drug resistance in ovarian cancer (Review)

Ovarian cancer is a fatal gynecological cancer and a major cause of cancer-related mortality worldwide. The main limitation to a successful treatment for ovarian cancer is the development of drug resistance to combined chemotherapy. Tumor suppressor genes (TSGs) are wild-type alleles of genes which play regulatory roles in diverse cellular activities, and whose loss of function contributes to the development of cancer. It has been demonstrated that TSGs contribute to drug resistance in several types of solid tumors. However, an overview of the contribution of TSGs to drug resistance in ovarian cancer has not previously been reported. In this study, 15 TSGs responding to drug resistance in ovarian cancer were reviewed to determine the relationship of TSGs with ovarian cancer drug resistance. Furthermore, gene/protein-interaction and bio-association analysis were performed to demonstrate the associations of these TSGs and to mine the potential drug resistance-related genes in ovarian cancer. We observed that the 15 TSGs had close interactions with each other, suggesting that they may contribute to drug resistance in ovarian cancer as a group. Five pathways/processes consisting of DNA damage, apoptosis, cell cycle, DNA binding and methylation may be the key ways with which TSGs participate in the regulation of drug resistance. In addition, ubiquitin C (UBC) and six additional TSGs including the adenomatous polyposis coli gene (APC), death associated protein kinase gene (DAPK), pleiomorphic adenoma gene-like 1 (PLAGL1), retinoblastoma susceptibility gene (RB1), a gene encoding an apoptosis-associated speck-like protein (PYCARD/ASC) and tumor protein 63 (TP63), which had close interactions with the 15 TSGs, are potential drug resistance-related genes in ovarian cancer.

The retinoblastoma protein (Rb) as an anti-apoptotic factor: expression of Rb is required for the anti-apoptotic function of BAG-1 protein in colorectal tumour cells

Although the retinoblastoma-susceptibility gene RB1 is inactivated in a wide range of human tumours, in colorectal cancer, the retinoblastoma protein (Rb) function is often preserved and the RB locus even amplified. Importantly, we have previously shown that Rb interacts with the anti-apoptotic Bcl-2 associated athanogene 1 (BAG-1) protein, which is highly expressed in colorectal carcinogenesis. Here we show for the first time that Rb expression is critical for BAG-1 anti-apoptotic activity in colorectal tumour cells. We demonstrate that Rb expression not only increases the nuclear localisation of the anti-apoptotic BAG-1 protein, but that expression of Rb is required for inhibition of apoptosis by BAG-1 both in a γ-irradiated Saos-2 osteosarcoma cell line and colorectal adenoma and carcinoma cell lines. Further, consistent with the fact that nuclear BAG-1 has previously been shown to promote cell survival through increasing nuclear factor (NF)-κB activity, we demonstrate that the ability of BAG-1 to promote NF-κB activity is significantly inhibited by repression of Rb expression. Taken together, data presented suggest a novel function for Rb, promoting cell survival through regulating the function of BAG-1. As BAG-1 is highly expressed in the majority of colorectal tumours, targeting the Rb–BAG-1 complex to promote apoptosis has exciting potential for future therapeutic development.

Double-edged sword: a p53 regulator mediates both harmful and beneficial effects in experimental acute kidney injury

Acute kidney injury triggers activation of innate immune responses and of proapoptotic programs such as the p53 pathway. Mulay et al. examine the effects of blocking murine double minute-2 (mdm2), a negative regulator of p53, using a novel chemotherapeutic agent, nutlin-3a, in mouse ischemia-reperfusion injury. Their results indicate that mdm2 promotes renal regeneration by limiting p53-mediated apoptosis but also enhances early inflammation by facilitating DNA binding of nuclear factor-κB independently of p53.

Chromosome instability and deregulated proliferation: an unavoidable duo.

The concept that aneuploidy is a characteristic of malignant cells has long been known; however, the idea that aneuploidy is an active contributor to tumorigenesis, as opposed to being an associated phenotype, is more recent in its evolution. At the same time, we are seeing the emergence of novel roles for tumor suppressor genes and oncogenes in genome stability. These include the adenomatous polyposis coli gene (APC), p53, the retinoblastoma susceptibility gene (RB1), and Ras. Originally, many of these genes were thought to be tumor suppressive or oncogenic solely because of their role in proliferative control. Because of the frequency with which they are disrupted in cancer, chromosome instability caused by their dysfunction may be more central to tumorigenesis than previously thought. Therefore, this review will highlight how the proper function of cell cycle regulatory genes contributes to the maintenance of genome stability, and how their mutation in cancer obligatorily connects proliferation and chromosome instability.

Abstract 266: Differential activation of the alkaline phosphatase promoter by pRB and p107

Abstract The retinoblastoma susceptibility gene, Rb1, is closely linked with osteosarcoma as well as retinoblastoma. Functional analysis of pRB and the closely related family members, p107 and p130, has tended to focus on repression of proliferation, but genetic evidence from our lab and others indicates an active requirement for pRB in osteoblast differentiation that correlates more directly with osteosarcoma susceptibility. Our prior studies linked the pRB family with activation of the early osteoblast marker, alkaline phosphatase (the product of the Alpl gene). We have shown by Chromatin immunoprecipitation (ChIP) analysis the Alpl promoter is targeted directly by pRB and p107 when active. We addressed the issue of the specific contribution of pRB with the use of shRNA to create stable knockdown of pRB in an osteoblast precursor line. These studies showed pRB is required for several activation events. pRB displaces the repressor histone demethylase, KDM5A, from the inactive promoter. pRB is also necessary for recruiting a BRG1containing SWI/SNF complex to the promoter, which in turn is required for the recruitment of RNA polymerase II. The presence of p107 on the active Alpl promoter suggests it also contributes to activation, even though p107 is not implicated in suppression of osteosarcoma. p107 is not sufficient for the pRB-dependent functions discussed above, but it is unknown whether p107 is necessary. We addressed this issue with the use of shRNA to create stable knockdown of p107 in the osteoblast precursors. Depletion of p107 resulted in impaired induction of alkaline phosphatase, revealing that p107 is also essential for activation. However, the p107 depleted line remained able to displace KDM5A, showing that the functions of pRB and p107 are distinct. We considered the possibility that p107 is required to recruit specific transactivators to the promoter. While transcription factors that target Alpl directly have not previously been identified, SP1 and RUNX2 are the most strongly implicated. ChIP assays show both RUNX2 and SP1 bound to the active promoter in parental cells. Depletion of pRB resulted in the failure of both factors to associate with the promoter, but depletion of p107 had no effect on their promoter occupation. However, in contrast to the dispensability of p107 in displacement of KDM5A and recruitment of RUNX2 and Sp1, depletion of p107 resulted in failure of recruitment of BRG1-SWI/SNF, and in SWI/SNF-dependent recruitment of RNA polymerase II. Thus, pRB and p107 are both required for activation of Alpl expression, but their roles are not entirely overlapping. Further study of osteogenic genes targeted by pRB and/or p107 during differentiation, and the contribution of each, will help to understand the specific requirement for pRB in suppression of osteosarcoma. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 266. doi:10.1158/1538-7445.AM2011-266

Abstract 2100: Role of pocket proteins in HPV-associated head and neck squamous cell carcinomas

Abstract High-risk human papillomaviruses(HPVs) are associated with a subset of head and neck squamous cell carcinomas (HNSCC) as well as most of cervical cancers. HPV type 16 (HPV-16), which is found in the vast majority of HPV-positive HNSCC, encodes for three oncogenes: E5, E6, and E7. Previously, we learned that HPV-16 E7 is the dominant oncoprotein in head and neck cancer in mice. More recently, we learned that tissue specific inactivation of the retinoblastoma-susceptibility gene, pRb, a well known cellular target of HPV E7 and a member of the “pocket protein’ family, was not sufficient to account fully for the oncogenic properties of E7 in HNSCC. E7 is known to inactivate not just pRb, but also other related cellular proteins, specifically p107 and p130. This led to our current study in which we have observed that the combined loss of pRb and p130, or pRb and p107 leads to increased susceptibility to head and neck cancers in comparison to mice conditionally disrupted only for pRb, yet are not sufficient to account fully for E7's oncogenic potential in HPV-associated head and neck carcinogenesis. Additionally, combinatorial loss of pRb and p130, or pRb and p107 partially mediates E7-induced acute phenotypes in head and neck epithelia. Taken together, our results indicate that the combined inactivation of two pocket proteins are not sufficient to fully recapitulate E7 oncogenic properties in HNSCC. We conclude that inactivation of all three pocket proteins is necessary to account for E7's carcinogenic properties in HNSCC or that other targets of E7 contribute to its carcinogenic potential in HNSCC. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2100. doi:10.1158/1538-7445.AM2011-2100

Transcriptional Activation by pRB and Its Coordination with SWI/SNF Recruitment

A central question in cancer biology is why most tumor susceptibility genes are linked with only limited types of cancer. Human germ-line mutation of the retinoblastoma susceptibility gene Rb1 is closely linked with just retinoblastoma and osteosarcoma, although the gene is universally expressed. Functional analysis of pRB and its close relatives, p107 and p130, has largely focused on their roles in repression of proliferation across all tissue types, but genetic evidence indicates an active requirement for pRB in osteoblast differentiation that correlates more directly with osteosarcoma susceptibility. Still, potential promoter targets of pRB and its role in normally differentiating osteoblasts remain insufficiently characterized. Here, an early marker of osteoblast differentiation, alkaline phosphatase, is identified as a direct promoter activation target of pRB. One role of pRB on this promoter is to displace the histone lysine demethylase KDM5A, thereby favoring trimethylation of H3K4, a promoter activation mark. A major new aspect of pRB-mediated transcriptional activation revealed in this promoter analysis is its role in recruitment of an activating SWI/SNF chromatin-remodeling complex. SWI/SNF is a critical coordinator of tissue-specific gene expression. In osteoblasts, SWI/SNF complexes containing the BRM ATPase repress osteoblast-specific genes to maintain the precursor state, whereas the alternative ATPase BRG1 distinguishes an activating SWI/SNF complex necessary for RNA polymerase-II recruitment. A switch from BRM to BRG1 on the alkaline phosphatase promoter marks the onset of differentiation and is accomplished in a precise two-step mechanism. Dissociation of BRM-containing SWI/SNF depends on p300, and association of BRG1-containing SWI/SNF depends on pRB.