Two Gq class G proteins are expressed in human keratinocytes

Ectopic expression of the heterotrimeric G15 protein in pancreatic carcinoma and its potential in cancer signal transduction

G15 is a heterotrimeric G protein selectively expressed in immature cell lineages in adult tissues that feature higher cell renewal potential. It promiscuously couples a wide variety of G protein-coupled receptors (GPCRs) to phospholipase C. Intriguingly, G15 is poorly affected by GPCR desensitization. We show here that G15 α-subunit (Gα15) supports sustained stimulation of PKD1 by a constitutively desensitized GPCR co-transfected over a negative cell background. Based on the fact that PKD1 is a multifunctional protein kinase activated by PKC and known for promoting oncogenic signaling, we hypothesized that, if expressed out of its natural cell context, G15 might promote tumor growth. A screening for Gα15 mRNA expression pointed to pancreatic carcinoma among different human cancer cell types and revealed significant expression in human tumor biopsies xenografted in mice. In addition, G15 ectopic presence could functionally contribute to the transformation process since siRNA-induced depletion of Gα15 in pancreatic carcinoma cell lines dramatically inhibited anchorage-independent growth and resistance to the lack of nutrients. Altogether, our findings suggest that G15 supports tumorigenic signaling in pancreas and hence it may be considered as a novel potential target for the therapy of this form of cancer.

Differential expression of a gene homologous to a G-alpha protein gene in neonatal mouse skin during development of hair follicles

The development of mouse hair follicles depends on the proliferation, differentiation and migration of epithelial matrix cells in the follicle bulb. In particular, induction of the proliferation of epithelial cells is thought to be signalled by the dermal papilla at the base of the bulb. Neonatal mouse skin is useful for studying changes in gene expression during development of the follicles, as the mitotic activity of skin cells changes shortly after birth. Using RNA differential display, a 248-bp message has been identified, which is expressed in the skin, specifically on day 2 and day 3 but not on day 4 after birth. Confirmation of expression of this gene by ribonuclease protection assay showed that strong expression is seen on day 2 and day 3, but weak expression is also shown on day 1, day 4 and day 5. In situ hybridization data revealed that it is mainly localized in the dermal papilla. Analysis of its nucleotide sequence showed 99% identity between nucleotide 2 and 232 of the mouse uncoupled S49 cell mRNA for stimulatory GTP-binding protein (G(S)) alpha subunit, suggesting it is a segment of G(S)alpha. As the G(S)alpha subunit is involved in transducing extracellular signals across the cell, the finding of its expression in the papilla suggests it may be a molecular signal to the induction of epithelial proliferation in the follicle bulb. Evidence of strong expression on day 2, at the time when the mitotic activity of epithelial matrix cells starts to increase, also suggests that the G(S)alpha is a potential candidate for involvement in the initiation of follicle growth.

Proteinase-activated receptor-2 in human skin: tissue distribution and activation of keratinocytes by mast cell tryptase

Proteinase-activated receptor-2 (PAR-2) is a G-protein coupled receptor. Tryptic proteases cleave PAR-2 exposing a tethered ligand (SLIGKV), which binds and activates the receptor. Although PAR-2 is highly expressed by cultured keratinocytes and is an inflammatory mediator, its precise localization in the normal and inflamed human skin is unknown, and the proteases that activate PAR-2 in the skin have not been identified. We localized PAR-2 in human skin by immunohistochemistry, examined PAR-2 expression by RT-PCR and RNA blotting, and investigated PAR-2 activation by mast cell tryptase. PAR-2 was localized to keratinocytes, especially in the granular layer, to endothelial cells, hair follicles, myoepithelial cells of sweat glands, and dermal dendritic-like cells. PAR-2 was also highly expressed in keratinocytes and endothelial cells of inflamed skin. PAR-2 mRNA was detected in normal human skin by RT-PCR, and in cultured human keratinocytes and dermal microvascular endothelial cells by Northern hybridization. Trypsin, tryptase and a peptide corresponding to the tethered ligand (SLIGKVNH2) increased [Ca2+]i in keratinocytes, measured using Fura-2/AM. Although tryptase-containing mast cells were sparsely scattered in the normal dermis, they were numerous in the dermis in atopic dermatitis, and in the dermis, dermal-epidermal border, and occasionally within the lower epidermis in psoriasis. Tryptase may activate PAR-2 on keratinocytes and endothelial cells during inflammation.

Signalling through the leukotriene B4 receptor involves both alphai and alpha16, but not alphaq or alpha11 G-protein subunits

COS-7 cells transfected with the leukotriene (LT) B4 receptor (BLTR) cDNA were unable to produce LTB4-induced inositol phosphates (IPs) in spite of the presence of endogenous Galphai, Galphaq and Galpha11 proteins. Co-transfection of BLTR with Galpha16, however, resulted in high levels of IP production, which were 17-, 10- and 6-fold higher than with co-transfected Galpha11, Galphaq and Galpha14, respectively. Co-transfection of BLTR with phospholipase C (PLC) beta2, on the other hand, resulted in efficient IP production and co-transfection of BLTR with both Galpha16 and PLCbeta2 resulted in a greater than additive response.