1,25-Dihydroxyvitamin D3 and macrophage colony-stimulating factor-1 synergistically phosphorylate talin

Identification of SH2B1β as a focal adhesion protein that regulates focal adhesion size and number

The adaptor protein SH2B1β participates in regulation of the actin cytoskeleton during processes such as cell migration and differentiation. Here, we identify SH2B1β as a new focal adhesion protein. We provide evidence that SH2B1β is phosphorylated in response to phorbol 12-myristate 13-acetate (PMA)-induced protein kinase C (PKC) activation and show that PMA induces a rapid redistribution of SH2B1β out of focal adhesions. We also show that growth hormone (GH) increases cycling of SH2B1β into and out of focal adhesions. Ser161 and Ser165 in SH2B1β fall within consensus PKC substrate motifs. Mutating these two serine residues into alanine residues abrogates PMA-induced redistribution of SH2B1β out of focal adhesions, decreases SH2B1β cycling into and out of focal adhesions in control and GH-stimulated cells, and increases the size of focal adhesions. By contrast, mutating Ser165 into a glutamate residue decreases the amount of SH2B1β in focal adhesions and increases the number of focal adhesions per cell. These results suggest that activation of PKC regulates SH2B1β focal adhesion localization through phosphorylation of Ser161 and/or Ser165. The finding that phosphorylation of SH2B1β increases the number of focal adhesions suggests a mechanism for the stimulatory effect on cell motility of SH2B1β.

Phosphatidylinositol 3,4,5-trisphosphate directs association of Src homology 2-containing signaling proteins with gelsolin

Podosomes are adhesion structures in osteoclasts and are structurally related to focal adhesions mediating cell motility during bone resorption. Here we show that gelsolin coprecipitates some of the focal adhesion-associated proteins such as c-Src, phosphoinositide 3-kinase (PI3K), p130(Cas), focal adhesion kinase, integrin alpha(v)beta(3), vinculin, talin, and paxillin. These proteins were inducibly tyrosine-phosphorylated in response to integrin activation by osteopontin. Previous studies have defined unique biochemical properties of gelsolin related to phosphatidylinositol 3,4,5-trisphosphate in osteoclast podosomes, and here we demonstrate phosphatidylinositol 3,4,5-trisphosphate/gelsolin function in mediating organization of the podosome signaling complex. Overlay and GST pull-down assays demonstrated strong phosphatidylinositol 3,4,5-trisphosphate-PI3K interactions based on the Src homology 2 domains of PI3K. Furthermore, lipid extraction of lysates from activated osteoclasts eliminated interaction between gelsolin, c-Src, PI3K, and focal adhesion kinase despite equal amounts of gelsolin in both the lipid-extracted and unextracted experiment. The cytoplasmic protein tyrosine phosphatase (PTP)-proline-glutamic acid-serine-threonine amino acid sequences (PEST) was also found to be associated with gelsolin in osteoclast podosomes and with stimulation of alpha(v)beta(3)-regulated phosphorylation of PTP-PEST. We conclude that gelsolin plays a key role in recruitment of signaling proteins to the plasma membrane through phospholipid-protein interactions and by regulation of their phosphorylation status through its association with PTP-PEST. Because both gelsolin deficiency and PI3K inhibition impair bone resorption, we conclude that phosphatidylinositol 3,4,5-trisphosphate-based protein interactions are critical for osteoclast function.

Regulation of osteoclast differentiation by fibroblast growth factor 2: stimulation of receptor activator of nuclear factor kappaB ligand/osteoclast differentiation factor expression in osteoblasts and inhibition of macrophage colony-stimulating factor function in osteoclast precursors

This study investigated the mechanism of direct and indirect actions of fibroblast growth factor 2 (FGF-2) on osteoclast differentiation using two mouse cell culture systems. In the coculture system of osteoblasts and bone marrow cells, FGF-2 stimulated osteoclast formation. This effect was decreased markedly by osteoprotegerin (OPG) or NS-398, a selective cyclo-oxygenase 2 (COX-2) inhibitor. FGF-2 (> or = 10(-9) M) stimulated receptor activator of nuclear factor kappaB ligand/osteoclast differentiation factor (RANKL/ODF) messenger RNA (mRNA) expression from 2 h to 7 days in cultured osteoblasts. NS-398 did not affect the early induction but decreased the later one, indicating that the later effect is mediated by COX-2 induction in osteoblasts. To study the direct action of FGF-2 on osteoclast precursors, we used mouse macrophage-like cell line C7 cells that can differentiate into osteoclasts in the presence of soluble RANKL/ODF (sRANKL/ODF) and macrophage colony-stimulating factor (M-CSF). Although osteoblasts expressed all FGF receptors (FGFR-1 to -4), only FGFR-1 was detected in C7 cells at various differentiation stages. FGF-2 alone or in combination with sRANKL/ODF did not induce osteoclastogenesis from C7 cells; however, FGF-2 from lower concentrations (> or = 10(-11) M) significantly decreased osteoclast formation induced by M-CSF in the presence of sRANKL/ODF. FGF-2 did not alter mRNA levels of M-CSF receptor (Fms) or RANK in C7 cells. Immunoprecipitation/ immunoblotting analyses revealed that tyrosine phosphorylation of several cellular proteins including Fms in C7 cells induced by M-CSF was inhibited by FGF-2 in the presence of sRANKL/ODF. We conclude that FGF-2 regulates osteoclast differentiation through two different mechanisms: (1) an indirect stimulatory action via osteoblasts to induce RANKL/ODF partly through COX-2 induction and prostaglandin production and (2) a direct inhibitory action on osteoclast precursors by counteracting M-CSF signaling.

Colony-stimulating factor-1 induces cytoskeletal reorganization and c-src-dependent tyrosine phosphorylation of selected cellular proteins in rodent osteoclasts

Colony-stimulating factor-1 (CSF-1) stimulates motility and cytoplasmic spreading in mature osteoclasts. Therefore, we examined the cellular events and intracellular signaling pathways that accompany CSF-1-induced spreading in normal osteoclasts. To explore the role c-src plays in these processes, we also studied osteoclasts prepared from animals with targeted disruption of the src gene. In normal osteoclasts, CSF-1 treatment induces rapid cytoplasmic spreading, with redistribution of F-actin from a well-delineated central attachment ring to the periphery of the cell. CSF-1 increases membrane phosphotyrosine staining in osteoclasts and induces the phosphorylation of several cellular proteins in cultured, osteoclast-like cells, including c-fms, c-src, and an 85-kD Grb2-binding protein. Src kinase activity is increased threefold after CSF-1 treatment. In src- cells, no attachment ring is present, and CSF-1 fails to induce spreading or a change in the pattern of F-actin distribution. Although c-fms becomes phosphorylated after CSF-1 treatment, the 85-kD protein is significantly less phosphorylated in src- osteoclast-like cells. These results indicate that c-src is critical for the normal cytoskeletal architecture of the osteoclast, and, in its absence, the spreading response induced by CSF-1 is abrogated, and downstream signaling from c-fms is altered.

Phorbol myristate acetate transactivates the avian beta 3 integrin gene and induces alpha v beta 3 integrin expression

1,25-Dihydroxyvitamin D3 (1,25(OH)2D3)transactivates the avian beta 3 integrin gene whose promoter contains at least two vitamin D response elements, one of which is in close proximity to a candidate AP1 site (TGACTCA). Since fos/jun and steroid hormones interact to regulate gene expression, we asked whether phorbol-12-myristate-13-acetate (PMA), which stimulates binding of fos/jun to AP1 sites, transactivates the avian beta 3 integrin gene and, if so, does the phorbol ester modulate 1,25(OH)2D3 induction of the gene. We find the candidate AP1 sequence comigrates with the consensus AP1 sequence on electromobility shift assay when incubated with recombinant c-jun protein. Furthermore, PMA prompts expression of beta 3 integrin mRNA in the avian monocytic line, HD11. The increase in message reflects transactivation of the beta 3 gene and is mirrored by plasma membrane appearance of the integrin heterodimer alpha v beta 3. Moreover, attesting to the functional significance of PMA-enhanced alpha v beta 3 expression, cells treated with concentrations of the phorbol ester that induce the beta 3 gene, spread extensively on plastic, an event blocked by an anti-alpha v antibody and a peptide mimetic known to inhibit alpha v beta 3-mediated cell attachment. Interestingly, co-addition of 1,25(OH)2D3 and PMA prompts greater expression of alpha v beta 3 than when the cells are exposed to either agent alone and PMA enhances 1,25(OH)2D3-induced beta 3 integrin mRNA expression. Thus, PMA and 1,25(OH)2D3 impact on the avian beta 3 integrin gene independently and in combination.