Disease relevance of Khdrbs1

• Ablation of the Sam68 RNA binding protein protects mice from age-related bone loss [1].
• We hypothesized that mutation in the p62 gene resulting in either deletion or premature termination of the UBA domain accounts for the elevated osteoclastic formation and bone resorption associated with PDB [2].
• p62 ubiquitin binding-associated domain mediated the receptor activator of nuclear factor-kappaB ligand-induced osteoclast formation: a new insight into the pathogenesis of Paget's disease of bone [2].
• Using this antiserum, p68 also was detected in other cell lines including mouse erythroleukemia and Sertoli cells; rat Leydig, ovary, and glioma cells; and Chinese hamster ovary cells [3].
• We have now examined the role of p68 in the interaction between the catalytic subunit of pol-alpha and hyperphosphorylated retinoblastoma protein (ppRb) and in the stimulation of the polymerase activity of pol-alpha by ppRb [4].

High impact information on Khdrbs1

• The p68 was physically associated with activated c-Src, and it bound to the SH3 domain of c-Src in vitro [5].
• Tyrosine-phosphorylated p68 was also present in mitotic extracts of normal cells, suggesting that its phosphorylation was not just a consequence of transformation [5].
• We determine here the potential role of the signaling adapter p62 in T-cell polarization [6].
• In this report, we identified three of these proteins: Shc, a signaling protein that couples membrane tyrosine kinases with Ras; p62, a protein which can bind to p21rasGAP; and heterogeneous nuclear ribonucleoprotein K, a pre-mRNA-binding protein [7].
• Molecular cloning of the mRNAs associated with Sam68 in mouse spermatocytes reveals a subset of genes that might be posttranscriptionally regulated by this RNA-binding protein during spermatogenesis [8].

Biological context of Khdrbs1

• Herein we have investigated the expression and function during mammalian male meiosis of Sam68, an RNA-binding protein implicated in several aspects of RNA metabolism [8].
• Both kinases associate with Sam68 in pachytene spermatocytes and phosphorylate the regulatory regions upstream and downstream of the Sam68 RNA-binding motif [8].
• Analysis of correlations between gene expression and behavioural data revealed connection between the level of mRNA for K homology domain containing, RNA binding, signal transduction associated 1 (Khdrbs1) and ATPase Na+/K+ alpha2 subunit (Atp1a2) with morphine self-administration and analgesic effects, respectively [9].
• Consistent with these results is evidence that cells undergoing mitosis show a dramatic reduction in the level of Sam68 protein [10].
• Whereas simple haploinsufficiency of Sam68 produced by insertion mutagenesis in a single chromosomal allele did not detectably affect cell growth, reduction of Sam68 protein to <25% of the wild type level was associated with anchorage-independent growth, defective contact inhibition, and the ability to form metastatic tumors in nude mice [10].

Anatomical context of Khdrbs1

• We also demonstrate that Sam68 shuttles between the nucleus and the cytoplasm in secondary spermatocytes, suggesting that it may promote translation of specific RNA targets during the meiotic divisions [8].
• During the meiotic divisions, Sam68 translocates to the cytoplasm where it is found associated with the polysomes [8].
• Sam68 expression and localization within the cells is stage specific: it is expressed in the nucleus of spermatogonia, it disappears at the onset of meiosis (leptotene/zygotene stages), and it accumulates again in the nucleus of pachytene spermatocytes and round spermatids [8].
• Here we report that RHKO-induced Sam68 deficiency results in neoplastic transformation of murine NIH3T3 fibroblasts [10].
• Fyn membrane localization is necessary to induce the constitutive tyrosine phosphorylation of Sam68 in the nucleus of T lymphocytes [11].

Associations of Khdrbs1 with chemical compounds

• Second, the phosphotyrosine content of p190 in cells overexpressing defective pp60c-src is reduced in comparison with wild-type (wt) c-src overexpressors, while that of p62 is significantly less affected [12].
• Cultures of mouse embryo fibroblasts generated from Sam68+/+ and Sam68-/- littermates were induced to differentiate into adipocytes with culture medium containing pioglitazone and the Sam68-/- mouse embryo fibroblasts shown to have impaired adipocyte differentiation [1].
• Purification of p68 was achieved by passage of a 100 000 X g supernatant fraction over DEAE-cellulose, fractionation with ammonium sulfate, and chromatography on hydroxylapatite [3].

Enzymatic interactions of Khdrbs1

• Sam68 is the major tyrosine-phosphorylated and Src-associated protein in mitotic cells [13].

Other interactions of Khdrbs1

• We find that Sam68 phosphorylation, including in the nuclear fraction in which the molecule is predominantly expressed, is lost with a delocalized Fyn mutant deleted of its N-terminal membrane-anchoring domain [11].
• RACK1 regulates Src-mediated Sam68 and p190RhoGAP signaling [14].
• Sam68 stimulates G1/S transition and this effect is dependent on the integrity of its KH domain (hnRNPK Homology) which confers nucleic acid binding properties [13].

Analytical, diagnostic and therapeutic context of Khdrbs1

• Radicicol reversibly inhibits the mitosis-specific tyrosine phosphorylation of Sam68 in vivo, as determined by antiphosphotyrosine immunoblotting [15].
• However, the interaction of Ras-GAP with Sam68 has been brought into question, based on the lack of co-immunoprecipitation between Sam68 and Ras-GAP in interphase cells [13].
• Immunofluorescence analysis showed that while either singly expressed p180 or p68 was localized in the cytoplasm, cotransfection of both subunits resulted in colocalization in the nucleus [16].
• Furthermore, as determined by confocal microscopy, deletion of the p62 UBA domain impaired the association of p62 with TRAF6 in the proteasomal compartment [2].
• Cell lines that reached the advanced stage of feeder-independent agar growth showed increased detection by antiphosphotyrosine Western blot of the GAP-associated p62 phosphoprotein as well as of a 55 kDa phosphoprotein while detection of the P160 v-abl phosphoprotein remained constant throughout all stages of progression [17].

References