Abstract 2476: Role of retinoblastoma gene in maintenance of osteoblast function and communication

Abstract

Abstract Retinoblastoma gene (Rb1) loss of function mutations is commonly seen in osteosarcomas resulting in poorly differentiated tumors. In addition to cell cycle regulation, Rb1 function has been shown to be important in cell fate determination. It is known that loss of Rb1 function in mesenchymal stem cells inhibits osteoblast differentiation and predisposes them towards adipocytic lineage. Recent studies have suggested a role for Rb1 in cell adhesion but mechanistic details are missing. As cadherin 11 (Cad11) and gap junctional protein connexin43 (Cx43), play important roles in adhesion and communication in osteoblasts, we studied these proteins in MC3T3-E1 mouse calvaria osteoblast cell line. We compared osteoblasts with reduced Rb1 expression to vector-transfected osteoblasts to assess the relationship between Rb1, Cad11, and Cx43. Decreased RNA and protein expression of Cad11 were noted during differentiation of Rb1 deficient osteoblasts when compared to controls. Gap junctional intercellular communication was also studied and found to be reduced with Rb1 loss. Rb1 deficient cells had a higher steady-state level of adipocyte transcription factors and adipocyte markers when compared to control. Interestingly no changes were observed in Cx43 mRNA or protein expression when comparing the two lines. Immunofluorescence analysis demonstrated that a decrease in Cad11 may have affected its co-localization with Cx43. This, in turn, may have affected the proper formation of intercellular channels and thereby communication. These observations suggest that loss of Rb1 affects adhesion and communication in osteoblasts resulting in the expression of an adipocyte phenotype. Citation Format: Elisha Pendleton, Anthony Ketner, Thomas Bodenstine, Nalini Chandar. Role of retinoblastoma gene in maintenance of osteoblast function and communication [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2476.