Src‐like adaptor protein regulates osteoclast generation and survival

Abstract

Src-like adaptor protein (SLAP) is a hematopoietic adaptor containing Src homology (SH)3 and SH2 motifs and a unique carboxy terminus. Unlike c-Src, SLAP lacks a tyrosine kinase domain. We investigated the role of SLAP in osteoclast development and resorptive function. Employing SLAP-deficient mice, we find lack of the adaptor enhances in vitro proliferation of osteoclast precursors in the form of bone marrow macrophages (BMMs), without altering their survival. Furthermore, osteoclastogenic markers appear more rapidly in SLAP−/− BMMs exposed to RANK ligand (RANKL). The accelerated proliferation of M-CSF-treated, SLAP-deficient precursors is associated with enhanced ERK activation. SLAP’s role as a mediator of M-CSF signaling, in osteoclastic cells, is buttressed by complexing of the adaptor protein and c-Fms in lipid rafts. Unlike c-Src, SLAP does not impact resorptive function of mature osteoclasts, but induces their early apoptosis. Thus, SLAP negatively regulates differentiation of osteoclasts and proliferation of their precursors. Conversely, SLAP decreases osteoclast death by inhibiting activation of caspase 3. These counterbalancing events yield indistinguishable bones of WT and SLAP−/− mice which contain equal numbers of osteoclasts in basal and stimulated conditions.

RTK SLAP DOWN: The emerging role of Src-like adaptor protein as a key player in receptor tyrosine kinase signaling

“…Shortly thereafter, Pakuts et al confirmed by Far Western analysis that SLAP2 directly associates with CSF-1R both before and after CSF-1 stimulation [46]. Notably, SLAP also bound CSF-1R [17,46], but in contrast to the constitutive association of SLAP2 with CSF-1R, SLAP interaction was strongly induced by CSF-1 stimulation [46]. This suggests that the molecular basis of the interaction between CSF-1R and SLAP or SLAP2 may differ.…”

“…SLAP mRNA is predominantly expressed in lymphoid tissues, including spleen, thymus, and lymph nodes, and is expressed in both primary T cells and primary B cells [16]. High levels of SLAP mRNA expression have also been detected in lung, fetal brain, and epithelial intestine, while moderate levels were detected in heart, adult brain, liver, skeletal muscle, kidney, placenta, pancreas, skin, and bone marrow macrophages [4,5,[17][18][19]. SLAP is expressed in a number of cell lines, including NIH3T3 fibroblasts [20], BaF3 pro-B cells [18], and P815 mastocytoma cells [21], and its expression can be induced in myeloidderived cell lines U937, HL60, and NB-4 by stimulation with all-trans retinoic acid [22].…”

“…Current data suggests that SLAP2 expression is predominantly hematopoietic [11], with expression in bone marrow macrophages [17], platelets [24], and purified human T cells, B cells, and monocytes [8]. SLAP2 is highly expressed in peripheral blood leukocytes, spleen, thymus, and lung, and expressed at low levels in small intestine, heart, skeletal muscle, colon, placenta, prostate, and skin [8][9][10].…”

“…Recruitment of SFKs and other SH2 domain-containing proteins to activated CSF-1R governs the proliferation, differentiation and survival of macrophages through activation of the MAP kinase cascade (Ras/ MEK/ERK) and Akt (reviewed in [44]). SLAP and SLAP2 mRNA are constitutively present in bone marrow macrophages [17,45], and evidence implicates both SLAP and SLAP2 as negative regulators of CSF-1 induced signaling.…”

“…Similarly, SLAP was shown to mediate CSF-1 stimulated signaling in primary osteoclasts [17]. Compared to BMMs isolated from WT mice, BMMs from SLAP −/− mice showed accelerated proliferation of osteoclast precursors and enhanced osteoclast formation [17].…”