title: Regulation of osteoblast gene expression in intratypic osteosarcoma hybrid cells.
abstract: Intratypic osteosarcoma hybrids were constructed by fusing the human osteoblast-like osteosarcoma SaOS-2 with the rat osteoblast-like osteosarcoma UMR-106. Both of these osteosarcomas express liver/bone/kidney alkaline phosphatase (ALPL), but only the UMR-106 cell line expresses osteopontin (OPN), a gene expressed during later stages of osteoblast differentiation. Analysis of osteoblast gene expression in these hybrids demonstrated that ALPL continued to be expressed; however, OPN steady-state mRNA levels were dramatically reduced in four hybrids. Quantitative measurements indicated that OPN steady-state mRNA levels were extinguished by a factor of 20- to 1000-fold. Since SaOS-2 chromosomes are preferentially lost from these hybrids, subclones of extinguished hybrids were isolated that reexpressed OPN mRNA at levels similar to the UMR-106 parental line. These data indicate that trans-acting negative regulatory factors, expressed from the SaOS-2 genome, are responsible for OPN extinction. This report provides the first demonstration of the negative regulation of OPN gene expression and also provides additional evidence that extinction plays a role in the regulation of osteoblast gene expression.
mesh_terms: D000469:Alkaline Phosphatase / Q000235:genetics*; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002454:Cell Differentiation; D004273:DNA, Neoplasm / Q000032:analysis; D005786:Gene Expression Regulation; D015972:Gene Expression Regulation, Neoplastic; D005796:Genes / Q000235:genetics; D006801:Humans; D006822:Hybrid Cells / Q000378:metabolism*; D008969:Molecular Sequence Data; D010006:Osteoblasts / Q000378:metabolism*; D053495:Osteopontin; D012516:Osteosarcoma; D012333:RNA, Messenger / Q000032:analysis; D012334:RNA, Neoplasm / Q000032:analysis; D051381:Rats; D012795:Sialoglycoproteins / Q000235:genetics*
chemical_list: D004273:DNA, Neoplasm; D012333:RNA, Messenger; D012334:RNA, Neoplasm; C506895:SPP1 protein, human; D012795:Sialoglycoproteins; C506897:Spp1 protein, rat; D053495:Osteopontin; D000469:Alkaline Phosphatase