Cutaneous manifestations in Costello syndrome: HRAS p.Gly12Ser affects RIN1-mediated integrin trafficking in immortalized epidermal keratinocytes

Heterozygous germline missense variants in the HRAS gene underlie Costello syndrome (CS). The molecular basis for cutaneous manifestations in CS is largely unknown. We used an immortalized human cell line, HaCaT keratinocytes, stably expressing wild-type or CS-associated (p.Gly12Ser) HRAS and defined RIN1 as quantitatively most prominent, high-affinity effector of active HRAS in these cells. As an exchange factor for RAB5 GTPases, RIN1 is involved in endosomal sorting of cell-adhesion integrins. RIN1-dependent RAB5A activation was strongly increased by HRAS(Gly12Ser), and HRAS-RIN1-ABL1/2 signaling was induced in HRAS(WT)- and HRAS(Gly12Ser)-expressing cells. Along with that, HRAS(Gly12Ser) expression decreased total integrin levels and enriched beta 1 integrin in RAB5- and EEA1-positive early endosomes. The intracellular level of active beta 1 integrin was increased in HRAS(Gly12Ser) HaCaT keratinocytes due to impaired recycling, whereas RIN1 disruption raised beta 1 integrin cell surface distribution. HRAS(Gly12Ser) induced co-localization of beta 1 integrin with SNX17 and RAB7 in early/sorting and late endosomes, respectively. Thus, by retaining beta 1 integrin in intracellular endosomal compartments, HRAS-RIN1 signaling affects the subcellular availability of beta 1 integrin. This may interfere with integrin-dependent processes as we detected for HRAS(Gly12Ser) cells spreading on fibronectin. We conclude that dysregulation of receptor trafficking and integrin-dependent processes such as cell adhesion are relevant in the pathobiology of CS.

Automated summary

This study investigated the molecular mechanism underlying the skin manifestations in patients with Costello syndrome caused by mutations in the HRAS gene. The findings suggested that HRAS signaling pathways are involved in the regulation of integrin trafficking and cell adhesion, which are crucial for the pathobiology of Costello syndrome.