Abundance of the Organic Anion-transporting Polypeptide OATP4A1 in Early-Stage Colorectal Cancer Patients: Association With Disease Relapse

SLCO4A1 expression is associated with activated inflammatory pathways in high-grade serous ovarian cancer

Patients with high-grade serous ovarian cancer (HGSOC) have a very poor overall survival. Current therapeutic approaches do not bring benefit to all patients. Although genetic alterations and molecular mechanisms are well characterized, the molecular pathological conditions are poorly investigated. Solute carrier organic anion transporter family member 4A1 (SLCO4A1) encodes OATP4A1, which is an uptake membrane transporter of metabolic products. Its expression may influence various signaling pathways associated with the molecular pathophysiological conditions of HGSOC and consequently tumor progression. RNA sequencing of 33 patient-derived HGSOC cell lines showed that SLCO4A1 expression was diverse by individual tumors, which was further confirmed by RT-qPCR, Western blotting and immunohistochemistry. Gene Set Enrichment Analysis revealed that higher SLCO4A1 level was associated with inflammation-associated pathways including NOD-like receptor, adipocytokine, TALL1, CD40, NF-κB, and TNF-receptor 2 signaling cascades, while low SLCO4A1 expression was associated with the mitochondrial electron transport chain pathway. The overall gene expression pattern in all cell lines was specific to each patient and remained largely unchanged during tumor progression. In addition, genes encoding ABCC3 along with SLCO4A1-antisense RNA 1, were associated with higher expression of the SLCO4A1, indicating their possible involvement in inflammation-associated pathways that are downstream to the prostaglandin E2/cAMP axis. Taken together, increased SLCO4A1/OATP4A1 expression is associated with the upregulation of specific inflammatory pathways, while the decreased level is associated with mitochondrial dysfunction. These molecular pathophysiological conditions are tumor specific and should be taken into consideration by the development of therapies against HGSOC.

Two common polymorphic variants of OATP4A1 as potential risk factors for colorectal cancer

Genetic variations in the organic-anion-transporting polypeptide (OATP)-encoding solute carrier of organic anions (SLCO) genes can promote cancer development and progression. The overexpression of solute carrier organic anion transporter family member 4A1 (OATP4A1), a transporter for steroid hormones, prostaglandins, and bile acids, has been previously associated with tumor recurrence and progression in colorectal cancer (CRC). Therefore, the present study aimed to investigate the association between 2 frequent single nucleotide polymorphisms (SNPs) in SLCO4A1 (rs34419428, R70Q; rs1047099G, V78I) and CRC predisposition. Following restriction fragment length polymorphism-PCR analysis in 178 patients with CRC [Union for International Cancer Control (UICC) stage I/II] and 65 healthy controls, no significant difference was observed in allele frequency and the number of heterozygous/homozygous individuals between the groups. Notably, the R70Q minor allele was identified to be associated with the V78I minor allele in the genome. Comparing of the individual genotypes of CRC patients to clinical data, including sex, UICC-stage and relapse revealed no increased risk for CRC. In addition, the OATP4A1 immunoreactivity assay in paraffin-embedded CRC and adjacent non-tumorous mucosa sections, examined using quantitative microscopy image analysis, did not reveal any association with these polymorphisms. No significant differences were observed in the expression levels, localization, and sodium fluorescein transport capacity among the OATP4A1 variants, which was studied using functional assays in Sf9-insect and A431 tumor cells overexpressing the 2 single and a double mutant OATP4A1 SNP variants. These results suggested that the 2 most frequent polymorphisms located in the first intracellular loop of OATP4A1 do not associate with CRC predisposition and tumor recurrence. They are unlikely to affect the outcome of CRC in patients.