Functional Calcium-sensing Receptors in Rat Fibroblasts Are Required for Activation of SRC Kinase and Mitogen-activated Protein Kinase in Response to Extracellular Calcium

Abstract

Changes in the concentration of extracellular calcium can affect the balance between proliferation and differentiation in several cell types, including keratinocytes, breast epithelial cells, and fibroblasts. This report demonstrates that elevation of extracellular calcium stimulates proliferation-associated signaling pathways in rat fibroblasts and implicates calcium-sensing receptors (CaR) as mediators of this response. Rat-1 fibroblasts express CaR mRNA and protein and respond to known agonists of the CaR with increased IP 3 production and release of intracellular calcium. Agonists of the CaR can stimulate increased c-SRC kinase activity and increased extracellular signal-regulated kinase 1/mitogen-activated protein kinase activity. Both of the increases in SRC activity and mitogen-activated protein kinase activation are blocked in the presence of a nonfunctional mutant of the CaR, R796W. Proliferation of wild-type Rat-1 cells is sensitive to changes in extracellular calcium, but expression of the nonfunctional CaR mutant or inhibition of the calcium-dependent increase in SRC kinase activity block the proliferative response to calcium. These results provide evidence of a novel signal transduction pathway modulating the response of fibroblasts to extracellular calcium and imply that calciumsensing receptors may play a role in regulating cell growth in response to extracellular calcium, in addition to their well known function in systemic calcium homeostasis.

The extracellular calcium sensing receptor is expressed in mouse mesangial cells and modulates cell proliferation

“…There are numerous reports showing the CaSRs' effect on cell proliferation in many cell types including myeloma (Yamaguchi et al, 2002), ovarian surface epithelial cells (Hobson et al, 2000), fibroblasts (McNeil et al, 1998) and osteoblasts (Dvorak et al, 2004). We also studied the CaSRstimulated mesangial proliferation ( Figure 4A).…”

“…Thus, the current findings that the CaSR activation evokes a mitogenic effect on the MMCs further support the notion that the CaSR is involved in this physiological process in a variety of cell types. Elevated CaSR expression may contribute to the action of growth signaling pathways, including mitogen-activated protein kinase (McNeil et al, 1998;Yamaguchi et al, 2002). In addition, many reports have shown that several protein kinases affect the CaSR-induced signaling cascades (Awata et al, 2001;Sakwe et al, 2004).…”

The stem cell niche in health and leukemic disease

“…We hypothesized that the stem cell may be able to recognize that extracellular calcium content. The calcium-sensing receptor (CaR) 17 is a seven membrane spanning receptor that does not serve as a channel to transport calcium, but recognizes extracellular calcium. In a null mouse model, in the absence of this receptor, the stem cells were unable to engraft at the endosteal surface in a competitive setting (see Figure 1).…”

Calcium-induced Matrix Metalloproteinase 9 Gene Expression Is Differentially Regulated by ERK1/2 and p38 MAPK in Oral Keratinocytes and Oral Squamous Cell Carcinoma

“…Changes in extracellular calcium are monitored by the ubiquitously expressed extracellular calcium-sensing receptor (CaR) (43,44). Calcium-or agonist-induced activation of this G protein-coupled receptor has been linked to activation of various MAP kinases, including ERK1/2 (45)(46)(47). Our preliminary data suggest that CaR activation with the polycationic agonist Gd 3ϩ can also induce MMP-9 gene expression (data not shown), suggesting that signaling through the CaR may control MMP-9 expression in premalignant oral keratinocytes.…”