Unraveling the Molecular Pathogenesis of Protein C Deficiency-Associated VTE: Insights from Protein C Mutations C238G and R189W in Thai Patients.

Protein C (PC) deficiency is a well-established risk factor for venous thromboembolism (VTE), often manifesting in pediatric patients. This study aimed to elucidate the pathogenic mechanisms underlying two novel PC mutations, C238G and R189W, identified in Thai children with VTE. Through transient transfection of HEK293T cells, the effects of the wild-type (WT), C238G, and R189W PC variants were investigated. The C238G mutation demonstrated a severe (95%) reduction in PC secretion, while the R189W showed a 30% decrease compared to WT. Immunofluorescence analysis revealed that the C238G-PC was predominantly localized in the endoplasmic reticulum (ER), suggesting intracellular retention due to protein misfolding. This was accompanied by a significant upregulation of ER stress-related genes in C238G-expressing cells, indicating the activation of the unfolded protein response (UPR). In contrast, the R189W mutation led to a modest upregulation of UPR genes, implying a less severe impact on protein folding and secretion. Structural analysis highlighted the critical role of the highly conserved C238 residue in maintaining the disulfide bond and 3D conformation essential for PC functionality. These findings provide insights into the distinct molecular pathogenic mechanisms by which the C238G and R189W mutations result in PC deficiency and increased thrombotic risk in affected individuals. This current study emphasizes the importance of the C238 residue in preserving PC structural integrity and secretion, contributing to our understanding of PC deficiency-associated VTE.