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BIGH3-induced Osteocyte Apoptosis and Gap Junction Failure Foster Osteolysis in Clear Cell Renal Cell Carcinoma (ccRCC) Bone Metastasis

ABSTRACT: Metastatic progression in bone involves crosstalk between tumor cells and osteoblasts, osteoclasts, and osteocytes. Renal cell carcinoma bone metastases (RCCBM) are predominantly osteolytic and often treatment resistant. We previously reported that inhibition of osteoblast differentiation by BIGH3 (transforming growth factor-beta-induced protein ig-h3) secreted by colonizing 786-O RCC cells promotes tumor progression in bone. Here we report that BIGH3 induces osteocyte apoptosis in both human specimens and mice and inhibits gap junction (GJ) protein Cx43 expression and function, disrupting bone homeostasis. As proof-of-concept, lysosomal inhibitors, such as hydroxychloroquine (HCQ) and NH4Cl, reversed BIGH3-mediated GJ dysfunction in vitro; and inhibited tumor growth and reversed Bo-786 RCC-induced osteolysis in vivo. HCQ in combination with CBZ, but not alone, reversed the RCCBM-mediated decreases in bone mineral density and osteoblast numbers, and decreased osteocyte apoptosis and osteoclast recruitment. These BIGH3 associated impacts on the bone microenvironment comprise a noncanonical mechanism of metastasis progression.

ORGANISM(S): Mus musculus

PROVIDER: GSE244453 | GEO | 2024/09/18

REPOSITORIES: GEO

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Project description:Although localized to the mineralized matrix of bone, osteocytes are able to respond to systemic factors such as the calciotropic hormones 1,25(OH)2D3 and PTH. In the present studies, we examine the transcriptomic response to PTH in an osteocyte cell model and found that this hormone regulated an extensive panel of genes. Surprisingly, PTH uniquely modulated two cohorts of genes, one that was expressed and associated with the osteoblast to osteocyte transition and the other a cohort that was expressed only in the mature osteocyte. Interestingly, PTH’s effects were largely to oppose the expression of differentiation-related genes in the former cohort, while potentiating the expression of osteocyte-specific genes in the latter cohort. A comparison of the transcriptional effects of PTH with those obtained previously with 1,25(OH)2D3 revealed a subset of genes that was strongly overlapping. While 1,25(OH)2D3 potentiated the expression of osteocyte-specific genes similar to that seen with PTH, the overlap between the two hormones was more limited. Additional experiments identified the PKA-activated phospho-CREB (pCREB) cistrome, revealing that while many of the differentiation-related PTH regulated genes were apparent targets of a PKA-mediated signaling pathway, a reduction in pCREB binding at sites associated with osteocyte-specific PTH targets appeared to involve alternative PTH activation pathways. That pCREB binding activities positioned near important hormone-regulated gene cohorts were localized to control regions of genes was reinforced by the presence of epigenetic enhancer signatures exemplified by unique modifications at histones H3 and H4. These studies suggest that both PTH and 1,25(OH)2D3 may play important and perhaps cooperative roles in limiting osteocyte differentiation from its precursors while simultaneously exerting distinct roles in regulating mature osteocyte function. Our results provide new insight into transcription factor-associated mechanisms through which PTH and 1,25(OH)2D3 regulate a plethora of genes important to the osteoblast/osteocyte lineage. ChIP-seq was performed on MC3T3-E1 cells for Phospho-Creb following 1 hour vehicle or forskolin treatment in biological replicate. Input sample was previously published in GSE41920 (http://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSM1027508).

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BIGH3-induced Osteocyte Apoptosis and Gap Junction Failure Foster Osteolysis in Clear Cell Renal Cell Carcinoma (ccRCC) Bone Metastasis

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