%0 PDF %T Impact of Retinoblastoma Protein Loss on Osteoblast Migration and Differentiation. %A Gunduz, Volkan. %D 2017-04-14T13:35:20.157Z %8 2017-04-14 %R http://localhost/files/8336hd19d %X Abstract: The retinoblastoma protein pathway is inactivated in a wide range of human cancers. RB1 itself, however, is frequently inactivated only in a subset of tumors including retinoblastoma and osteosarcoma (OS). The fact that RB1 loss favors tumor formation in certain tissues suggests that pRB might have tissue-specific functions in addition to its central role in cell cycle regulation. Indeed pRB is crucial for both commitment to the osteoblast lineage and late stages of osteoblast differentiation. RB1 knockout (KO) calvarial osteoblasts contain an increased pool of osteoprogenitors that could differentiate into adipocytes as well as osteoblasts. In addition, pRB interacts with RUNX2 and enhances RUNX2-dependent transcription of osteoblast- specific genes. One characteristic of OS as well as other tumors in which RB1 is frequently inactivated is the lack of N-cadherin mediated cell-cell adhesions as a result of alterations in the expression and localization of N-cadherin. In contrast to OS, N-cadherin is highly expressed in osteoblasts and important for osteoblast differentiation and function. Perturbation of these interactions impairs in vitro mineralization of osteoblasts and osteoblast-specific gene expression. Therefore loss of N-cadherin-mediated cell-cell adhesions could contribute to the undifferentiated and invasive nature of osteosarcoma. The frequent inactivation of RB1 and parallel loss of N-cadherin expression in OS prompted me to ask whether these observations are directly related to each other. In this study I observed reduced N-cadherin expression in germline RB1 KO calvarial osteoblasts. In addition, we sought to understand if low N-cadherin expression affected migration and contributed to the adipogenic potential of RB1 KO osteoblasts. Whereas primary RB1 KO osteoblasts were not necessarily more migratory, RB1 KO cell lines derived from primary osteoblasts had increased migration potential compared to RB1 WT counterparts. These altered migratory properties of RB1 KO osteoblasts showed a dependence on IGF-I expression and receptor signaling, which are potentially intrinsic to the progenitor cells immortalized upon loss of pRB (expression). We demonstrate that adipogenic potential in RB1 KO cell lines is correlated with N-cadherin expression. Cell lines that undergo adipogenic differentiation downregulate N-cadherin expression, whereas those that don't maintain high levels of N-cadherin. We also show that individual RB1 KO cell lines consist of cells with varying degrees of N-cadherin expression, and adipogenic potential is enriched in the N-cadherin low population. Finally we show that acute loss of pRB doesn't affect N-cadherin expression or migration nor confer adipogenic potential to RB WT calvarial cells. Our findings suggest that these traits are properties of a particular cell type rather than a direct consequence of pRB loss. We propose that during osteoblast differentiation there is a transient cell state with low N-cadherin expression and this is maintained by IGF-I in an autocrine or paracrine fashion. Low N-cadherin expression could allow this cell to adopt either osteogenic or adipogenic fate and prime this cell for migration which could become apparent with additional alterations. Loss of pRB at this stage will prevent proper differentiation and deregulate cell cycle control resulting in the persistence and expansion of this cell type. Additional mutations could transform these cells and lead to osteosarcoma formation.; Thesis (Ph.D.)--Tufts University, 2011.; Submitted to the Dept. of Genetics.; Advisor: Philip Hinds.; Committee: Richard Etten, Charlotte Kuperwasser, and Grace Gill.; Keyword: Genetics. %[ 2022-10-11 %9 Text %~ Tufts Digital Library %W Institution