👤 Konstantinos Lefkimmiatis

The improper expression of glucose-dependent insulinotropic polypeptide receptor (GIPR) and the GIP/GIPR axis activation has been increasingly recognized in endocrine tumors, with a potential diagnostic and prognostic value. A high tumor-to-normal tissue ratio (T/N ratio) of GIPR was reported both in humans' and in rats' medullary thyroid cancer (MTC), suggesting a direct link between the neoplastic transformation and the mechanism of receptor overexpression. In this study, we evaluated the potential diagnostic and prognostic significance of GIPR expression in a large cohort of MTC patients by correlating GIPR mRNA steady-state levels to clinical phenotypes. The molecular effect of GIP/GIPR axis stimulation in MTC-derived cells was also determined. We detected GIPR expression in ~80% of tumor specimens, especially in sporadic, larger, advanced-stage cancers with higher Ki-67 values. GIPR stimulation induced cAMP elevation in MTC-derived cells and a small but significant fluctuation in Ca2+, both likely associated with increased calcitonin secretion. On the contrary, the effects on PI3K-Akt and MAPK-ERK1/2 signaling pathways were marginal. To conclude, our data confirm the high T/N GIPR ratio in MTC tumors and suggest that it may represent an index for the degree of advancement of the malignant process. We have also observed a functional coupling between GIP/GIPR axis and calcitonin secretion in MTC models. However, the molecular mechanisms underlying this process and the possible implication of GIP/GIPR axis activation in MTC diagnosis and prognosis need further evaluation. Show less

Melanocortin receptor-4 (MC4R) gene mutations are associated with early-onset severe obesity, and the identification of potential pathological variants is crucial for the clinical management of patients with obesity. To explore whether and how a novel heterozygous MC4R variant (MC4R-F313Sfs*29), identified in a young boy (body mass index [BMI] 38.8 kg/m2) during a mutation analysis conducted in a cohort of patients with obesity, plays a determinant pathophysiological role in the obesity development. The genetic screening was carried out in a total of 209 unrelated patients with obesity (BMI ≥ 35 kg/m2). Structural and functional characterization of the F313Sfs*29-mutated MC4R was performed using computational approaches and in vitro, using HEK293 cells transfected with genetically encoded biosensors for cAMP and Ca2+. The F313Sfs*29 was the only variant identified. In vitro experiments showed that HEK293 cells transfected with the mutated form of MC4R did not increase intracellular cAMP or Ca2+ levels after stimulation with a specific agonist in comparison with HEK293 cells transfected with the wild type form of MC4R (∆R/R0 = -90% ± 8%; P < 0.001). In silico modeling showed that the F313Sfs*29 mutation causes a major reorganization in the cytosolic domain of MC4R, thus reducing the affinity of the putative GalphaS binding site. The newly discovered F313Sfs*29 variant of MC4R may be involved in the impairment of α-MSH-induced cAMP and Ca2+ signaling, blunting intracellular G protein-mediated signal transduction. This alteration might have led to the dysregulation of satiety signaling, resulting in hyperphagia and early onset of obesity. Show less