TP53 and Let-7a micro-RNA Regulate K-Ras Activity in HCT116 Colorectal Cancer Cells

Abstract

Recent reports have indicated that KRAS and TP53 mutations predict response to therapy in colorectal cancer. However, little is known about the relationship between these two common genetic alterations. Micro-RNAs (miRNAs), a class of noncoding RNA implicated in cellular processes, have been increasingly linked to KRAS and TP53. We hypothesized that lethal-7a (let-7a) miRNA regulates KRAS through TP53. To investigate the relationship between KRAS, TP53, and let-7a, we used HCT116 KRASmut human colorectal cancer cells with four different genotypic modifications in TP53 (TP53−/−, TP53+/−, TP53mut/+, and TP53mut/−). Using these cells we observed that K-Ras activity was higher in cells with mutant or knocked out TP53 alleles, suggesting that wild-type TP53 may suppress K-Ras activity. Let-7a was present in HCT116 KRASmut cells, though there was no correlation between let-7a level and TP53 genotype status. To explore how let-7a may regulate K-Ras in the different TP53 genotype cells we used let-7a inhibitor and demonstrated increased K-Ras activity across all TP53, thus corroborating prior reports that let-7a regulates K-Ras. To assess potential clinical implications of this regulatory network, we examined the influence of TP53 genotype and let-7a inhibition on colon cancer cell survival following chemoradiation therapy (CRT). We observed that cells with complete loss of wild-type TP53 alleles (−/− or −/mut) were resistant to CRT following treatment with 5-fluorouracil and radiation. Further increase in K-Ras activity with let-7a inhibition did not impact survival in these cells. In contrast, cells with single or double wild-type TP53 alleles were moderately responsive to CRT and exhibited resistance when let-7a was inhibited. In summary, our results show a complex regulatory system involving TP53, KRAS, and let-7a. Our results may provide clues to understand and target these interactions in colorectal cancer.

Coffee reduces KRAS expression in Caco-2 human colon carcinoma cells via regulation of miRNAs

“…Previous studies have revealed that several miRNAs are involved in the regulation of KRAS gene expression in colorectal cancers (14,15). A preliminary microarray analysis of Caco-2 cell miRNAs following treatment with 2.5% coffee extract indicated that coffee induced expression of miR-30c and miR-96, which are known to target the KRAS gene (data not shown).…”

Transient gene and microRNA expression profile changes of confluent human fibroblast cells in spaceflight

“…Known as a tumor suppressor miRNA, Let‐7a has been found to inhibit the growth of several tumor types, including osteosarcoma cells and breast cancer cells (54, 55); thus, our observation of increased cell proliferation in the flown cells was consistent with the down‐regulation of Let‐7a. Although the involvement of Let‐7a in changes in gravity has not been reported previously, it has been reported that radiation exposure and other stress factors induce changes in the Let‐7 family, and such changes are p53 dependent (56). Down‐regulation of Let‐7a has been reported in fibroblast cells (AG1522) used in the present study after exposure to g ray and UV ray radiation (57); however, it is unclear whether exposure to space radiation caused the change in Let‐7a expression in the present study.…”

Biomarkers in colorectal liver metastases

“…Both TP53 and APC are tumour suppressor genes. A TP53 inhibits activated RAS through lethal (Let) 7a 23 . In the presence of TP53 mutation, Let-7a is not able to regulate activated RAS.…”