La Rovere, R. | bioRxiv Science

bioRxiv2024

Oncogenic GNAQ/11-induced remodeling of the IP3/Calcium signaling pathway protects Uveal Melanoma against Calcium-driven cell death

Despite being considered a rare tumor, uveal melanoma (UVM) is the most common adult intraocular malignancy. With a poor prognosis and limited treatment options, up to 50% of patients develop metastases, primarily in the liver. A range of mutations and chromosomal aberrations with significant prognostic value has been associated with UVM pathogenesis. The most frequently mutated genes are GNAQ and GNA11, which encode the subunits of Gq proteins and are described as driver mutations that activate multiple signaling cascades involved in cell growth and proliferation. Directly downstream of Gq/11 activation, PLC{beta} engagement leads to sustained production of DAG and IP3. While the DAG/PKC/RasGRP3/MAPK signaling branch has been identified as an essential component of UVM unregulated proliferation, the role of IP3-mediated signals has been largely overlooked. Here, we demonstrate that, whilst maintaining Ca{superscript 2} homeostasis, UVM cells have developed a decoupling mechanism between IP3 and ER Ca{superscript 2} release by altering IP3 receptor (IP3R) expression. This correlation was observed in human UVM tumors, where IP3Rs were found to be downregulated. Critically, when IP3R3 expression was restored, UVM cells exhibited an increased tendency to undergo spontaneous cell death and became more sensitive to pro-apoptotic modulators of IP3R-mediated Ca{superscript 2} signaling, such as staurosporine and the Bcl2-IP3R disrupter peptide BIRD2. Finally, inhibition of the Gq/11 signaling pathway revealed that IP3R expression is negatively regulated by GNAQ/11 oncogenic activation. Hence, we demonstrated that by remodeling IP3R expression, GNAQ/11 oncogenes protect UVM cells against IP3-triggered Ca{superscript 2} overload and cell death. Therefore, the GNAQ/11 pathway not only drives proliferation through DAG activity but also provides a protective mechanism to evade IP3/Ca{superscript 2}-mediated cell death. These dual functions could potentially be exploited in novel combinatorial therapeutic strategies to effectively block UVM cell proliferation while simultaneously sensitizing them to cell death.

cancer biology↗

bioRxiv2024

IP3 receptor depletion in a spontaneous canine model of Charcot-Marie-Tooth disease 1J with amelogenesis imperfecta

Inositol 1,4,5-trisphosphate receptors (IP3R) mediate Ca2+ release from intracellular stores, contributing to complex regulation of numerous physiological responses. The involvement of the three IP3R genes (ITPR1, ITPR2 and ITPR3) in inherited human diseases has started to shed light on the essential roles of each receptor in different human tissues and cell types. Variants in the ITPR3 gene, which encodes IP3R3, have recently been found to cause demyelinating sensorimotor Charcot-Marie-Tooth neuropathy type 1J (CMT1J). In addition to peripheral neuropathy, immunodeficiency and tooth abnormalities are occasionally present. Here, we report the identification of a homozygous nonsense variant in the ITPR3 gene in Lancashire Heeler dogs, presenting with a severe developmental enamel defect and reduced nerve conduction velocity. We studied the primary skin fibroblasts of the affected dogs and observed that the nonsense variant in ITPR3 led to a complete absence of full-length IP3R3 protein. Unexpectedly, the protein levels of IP3R1 and IP3R2 were also markedly decreased, suggesting co-regulation. Functional Ca2+ measurements revealed reduced IP3R-mediated Ca2+ flux upon stimulation of G-protein-coupled-receptors in the affected dog fibroblasts. We were able to rescue the IP3R1 and IP3R2 depletion by proteasome inhibition but not the IP3R3 loss, which was facilitated by nonsense-mediated mRNA decay. These findings highlight the first spontaneous mammalian phenotype caused by a nonsense variant in ITPR3, leading to the loss of IP3R3. The human and canine IP3R3 proteins are highly similar, and our study suggests that the tissue involvement resulting from the receptors dysfunction is also conserved. In summary, IP3R3 is critical for enamel formation and peripheral nerve maintenance. Author summaryWe investigated pet dogs, Lancashire Heelers, with impairments in tooth development and in the nerves that regulate limb muscles. Through genetic studies of the dog pedigree, we found that the phenotypes were caused by a recessively inherited mutation in the ITPR3 gene, which encodes one of three IP3 receptors (IP3R) isoforms (IP3R3 isoform) that are needed for intracellular Ca2+ signaling. Mutated IP3R3 has been recently linked to a human inherited neuropathy called Charcot-Marie-Tooth disease type 1J, which impairs peripheral nerve function and is accompanied by immunodeficiency and abnormal teeth in some individuals. We showed that in the skin cells of the affected dogs, the full-length IP3R3 protein was completely absent, and also the protein levels of the other two IP3R isoforms (IP3R1 and IP3R2) were severely lowered. This led to impaired agonist-induced Ca2+ release and signaling. Our results demonstrate the high conservation between human and canine IP3 receptors and their significance for different tissue systems. The genetic studies now highlight that IP3R3 is vital for peripheral nerve function and enamel development.

genetics↗