Evaluation of STAT5A Gene Expression in Aflatoxin B1 Treated Bovine Mammary Epithelial Cells

When less is more: The association between the expression of polymorphic CYPs and AFB1-induced HCC

BACKGROUND

An individual's genetic fingerprint is emerging as a pivotal predictor of numerous disease- and treatment-related factors. Single nucleotide polymorphisms (SNPs) in drug-metabolizing enzymes play key roles in an individual's exposure to a malignancy-associated risk, such as Aflatoxin B1 (AFB1)-induced hepatocellular carcinoma (HCC).

AIM

This study aimed at reviewing literature on the polymorphisms that exist in CYP enzymes and their possible link with susceptibility to AFB1-induced HCC.

MATERIALS & METHODS

A set of keywords associated with the study subject of interest was used to search the Google Scholar and the PubMed database. The last ten years' worth of research projects were included in the results filter. The research involved HCC patients and any connection between polymorphic forms of CYP enzymes and their susceptibility to AFB1-induced HCC, including older but significant data.

RESULTS

Variations in CYP1A2 and CYP3A4 were reported to impact the rate and magnitude of AFB1 bio-activation, thus influencing an individual's vulnerability to develop HCC. In HCC patients, the activity of CYP isoforms varies, where increased activity has been reported with CYP2C9, CYP2D6, and CYP2E1, while CYP1A2, CYP2C8, and CYP2C19 exhibit decreased activity. CYP2D6*10 frequency has been discovered to differ considerably in HCC patients. Rs2740574 (an upstream polymorphism in CYP3A4 as detected in CYP3A4*1B) and rs776746 (which affects CYP3A5 RNA splicing), both of which influence CYP3A expression, thus impacting the variability of AFB1-epoxide adducts in HCC patients.

DISCUSSION

CYP1A2 is the primary enzyme accountable for the formation of harmful AFBO globally. CYP3A4, CYP3A5, CYP3A7, CYP2B7, and CYP3A3 are also implicated in the bio-activation of AFB1 to mutagenic metabolites. It is thought that CYP3A4 is the protein that interacts with AFB1 metabolism the most.

CONCLUSION

Polymorphic variants of CYP enzymes have a functional impact on the susceptibility to AFB1-induced HCC. Outlining such variation and their implications may provide deeper insights into approaching HCC in a more personalized manner for guiding future risk-assessment, diagnosis, and treatment.

Aflatoxin B1 inhibits the type 1 interferon response pathway via STAT1 suggesting another mechanism of hepatocellular carcinoma

BACKGROUND

Aflatoxin B1 (AFB1) contamination of food is very high in most sub-Saharan African countries. AFB1 is known to cause hepatocellular carcinoma (HCC) by inducing mutation in the tumour suppressor gene TP53. The number of new HCC cases is high in West Africa with an accompanying high mortality. The type I interferon (IFN) pathway of the innate immune system limits viral infections and exerts its anti-cancer property by up-regulating tumour suppressor activities and pro-apoptotic pathways. Indeed, IFN-α is reported to show significant protective effects against hepatic fibrogenesis and carcinogenesis. However, the mechanism behind AFB1 deregulation of the type I interferon (IFN) signalling pathway, with consequent HCC is largely unknown. This current study seeks to test the hypothesis that AFB1 inhibits the type I IFN response by directly interfering with key signalling proteins and thus increase the risk of HCC in humans.

METHODS

We evaluated the effects of AFB1 on the type I IFN signalling pathway using IFN stimulated response element (ISRE)-based luciferase reporter gene assay. In addition, the effects of AFB1 on the transcript levels of JAK1, STAT1 and OAS3 were assessed by real-time quantitative polymerase chain reaction (RT-qPCR) and confirmed by immunoblot assay.

RESULTS

Our results indicated that AFB1 inhibited the type I IFN signalling pathway in human hepatoma cell line HepG2 cells by suppressing the transcript levels of JAK1, STAT1 and OAS3. AFB1 also decreased the accumulation of STAT1 protein.

CONCLUSION

The inhibition of the type I IFN anti-cancer response pathway by AFB1 suggest a novel mechanism by which AFB1 may induce hepatocellular carcinoma in humans.