The duration as well as the magnitude of mitogenactivated protein kinase activation has been proposed to regulate gene expression and other specific intracellular responses in individual cell types. Activation of ERK1/2 by the hypothalamic neuropeptide gonadotropin-releasing hormone (GnRH) is relatively sustained in ␣T3-1 pituitary gonadotropes and HEK293 cells but is transient in immortalized GT1-7 neurons. Each of these cell types expresses the epidermal growth factor receptor (EGFR) and responds to EGF stimulation with significant but transient ERK1/2 phosphorylation. However, GnRH-induced ERK1/2 phosphorylation caused by EGFR transactivation was confined to GT1-7 cells and was attenuated by EGFR kinase inhibition. Neither EGF nor GnRH receptor activation caused translocation of phospho-ERK1/2 into the nucleus in GT1-7 cells. In contrast, agonist stimulation of GnRH receptors expressed in HEK293 cells caused sustained phosphorylation and nuclear translocation of ERK1/2 by a protein kinase C-dependent but EGFR-independent pathway. GnRH-induced activation of ERK1/2 was attenuated by the selective Src kinase inhibitor PP2 and the negative regulatory C-terminal Src kinase in GT1-7 cells but not in HEK293 cells. In GT1-7 cells, GnRH stimulated phosphorylation and nuclear translocation of the ERK1/2-dependent protein, p90 RSK-1 (RSK-1). These results indicate that the duration of ERK1/2 activation depends on the signaling pathways utilized by GnRH in specific target cells. Whereas activation of the G q /protein kinase C pathway in HEK293 cells causes sustained phosphorylation and translocation of ERK1/2 to the nucleus, transactivation of the EGFR by GnRH in GT1-7 cells elicits transient ERK1/2 signals without nuclear accumulation. These findings suggest that transactivation of the tightly regulated EGFR can account for the transient ERK1/2 responses that are elicited by stimulation of certain G protein-coupled receptors.

In rat hepatic C9 cells, angiotensin II (Ang II)-induced activation of angiotensin type 1 (AT 1 ) receptors (AT 1 -Rs) stimulates extracellular signal-regulated kinase (ERK) 1/2 phosphorylation via transactivation of the endogenous epidermal growth factor (EGF) receptor (EGF-R) by a protein kinase C (PKC) ␦/Src/Pyk2-dependent pathway. This leads to phosphorylation of the EGF-R as well as its subsequent internalization. On the other hand, EGF-induced activation of the EGF-R in C9 cells was found to cause phosphorylation of the AT 1 -R. This was prevented by selective inhibition of the intrinsic tyrosine kinase activity of the EGF-R by AG1478 [4-(3Ј-chloroanilino)-6,7-dimethoxy-quinazoline] and was reduced by inhibition of PKC and phosphoinositide 3-kinase. EGF-induced AT 1 -R phosphorylation was associated with a decrease in membrane-associated AT 1 -Rs and a reduced inositol phosphate response to Ang II. Agonist activation of endogenous AT 1 -Rs and EGF-Rs induced the formation of a multireceptor complex containing both the AT 1 -R and the transactivated EGF-R. The dependence of these responses on caveolin was indicated by the finding that cholesterol depletion of C9 cells abolished Ang II-induced inositol phosphate production, activation of Akt/PKB and ERK1/2, and AT 1 -R internalization. Confocal microscopy demonstrated that caveolin-1 was endogenously phosphorylated and was distributed on the plasma membrane in patches that undergo redistribution during Ang II stimulation. Agonist-induced phosphorylation and association of caveolin 1 with the AT 1 -R was observed, consistent with a scaffolding role of caveolin during transactivation of the EGF-R by Ang II. The EGF-induced AT 1 -R/caveolin association was abolished by AG1478, suggesting that activation of the EGF-R promotes the association of caveolin and the AT 1 -R.

Numerous external stimuli, including G protein-coupled receptor agonists, cytokines, growth factors, and steroids activate mitogen-activated protein kinases (MAPKs) through phosphorylation of the epidermal growth factor receptor (EGF-R). In immortalized hypothalamic neurons (GT1-7 cells), agonist binding to the gonadotropin-releasing hormone receptor (GnRH-R) causes phosphorylation of MAPKs that is mediated by protein kinase C (PKC)-dependent transactivation of the EGF-R. An analysis of the mechanisms involved in this process showed that GnRH stimulation of GT1-7 cells causes release/shedding of the soluble ligand, heparin binding epidermal growth factor (HB-EGF), as a consequence of metalloprotease activation. GnRH-induced phosphorylation of the EGF-R and, subsequently, of Shc, ERK1/2, and its dependent protein, p90 RSK-1 (p90 ribosomal S6 kinase 1 or RSK-1), was abolished by metalloprotease inhibition. Similarly, blockade of the effect of HB-EGF with the selective inhibitor CRM197 or a neutralizing antibody attenuated signals generated by GnRH and phorbol 12-myristate 13-acetate, but not those stimulated by EGF. In contrast, phosphorylation of the EGF-R, Shc, and ERK1/2 by EGF and HB-EGF was independent of PKC and metalloprotease activity. The signaling characteristics of HB-EGF closely resembled those of GnRH and EGF in terms of the phosphorylation of EGF-R, Shc, ERK1/2, and RSK-1 as well as the nuclear translocation of RSK-1. However, neither the selective Src kinase inhibitor PP2 nor the overexpression of negative regulatory Src kinase and dominant negative Pyk2 had any effect on HB-EGF-induced responses. In contrast to GT1-7 cells, human embryonic kidney 293 cells expressing the GnRH-R did not exhibit metalloprotease induction and EGF-R transactivation during GnRH stimulation. These data indicate that the GnRH-induced transactivation of the EGF-R and the subsequent ERK1/2 phosphorylation result from ectodomain shedding of HB-EGF through PKC-dependent activation of metalloprotease(s) in neuronal GT1-7 cells.

Cases of Diabetes II have been rising in Saudi population. The main objective of our study was to analyze the relationship between the inheritance of ABO blood group and Rh factors and the development of type 2 diabetes (T2DM) in male population of Hail region of Saudi Arabia. Random community survey of about 200 local educated youth (under 18) and non-college going adults revealed high prevalence of diabetes II among adult male population (27.5%) as compared to the educated youth population (5.5%).In this study we first looked at the distribution of ABO and Rhesus (Rh) blood group antigen data of 490 non diabetic control group (283 females (57.7%) and 207 (42.4%) male and compared it with 342 diabetes type 2 patients (214 females and 128 male) who were admitted to the Diabetic clinic of King Khaled Hospital in Hail Saudi Arabia between 2008 and 2015. Out of 342 patients 214 (62.6%) were females and 128 (37.4 %) were males.Our results show that out of 207 control non diabetic individuals (males only) 6 were A-(2.89%), 43 were A+ (20.8%), 2 were AB-(0.96%), 9 were AB+ (4.3%), 7 were B-(3.38%), 44 were B+ (21.2%), 7 were O-(3.4%) and 89 were O+ (42.9%). So in control population O+ was the most prevalent blood group (42.9%) and B+ was the second most prevalent blood type (21.2%).Next we wanted to see if the blood group distribution patterns are similar among T2DM patients. Analysis of our results show that 2.3% of T2DM male patients were A-, 22.65% were A+, 0% were AB-, 4.7% were AB+, 0% were B-but 30.5% were B+ as compared to the 21.2% B+ among control group. Only 0.78% were Oand 39.1% were O+. When we looked at the distribution of Rh antigen in the control population we found 89.4% people to be Rh+ and 10.6% Rh-however among diabetics 96.9% patients were Rh+ and 3.13% were Rh-. These results suggest a 3.4 fold decrease in Rh-individuals among diabetics (3.13% Rh-) as compared to the control population (10.9% Rh-). So in conclusion percentage of Rh-individuals among T2DM male patients is reduced by 3.4 fold (3.13% Rh-) as compared to the control group (10.6% Rh-). Our results also show that blood group B+ is expressed in much higher percentage in diabetics (30.5%) as compared to the controls (21.2%). Additionally O+ is expressed in 42.9% controls but show a slight yet significant reduction in its distribution (39%) among T2DM patients. These results suggest that B+ offers least resistance to male T2DM patients and O+ provides a slight resistance to diabetes.