Targeting MALAT1 in hepatocellular carcinoma : therapeutic opportunities from herbal medicine

Abstract

The current therapies for hepatocellular carcinoma (HCC) are inefficient in completely eradicating the tumour cells. The resistance to cell death accounts largely for the aggressive genotype and phenotype of HCC. Recently, the dysregulation of long non-coding RNA has been proposed as one of the effectors for HCC progression; thus, aiming at the long non-coding RNA that are abnormally modulated may offer new therapy for HCC management. Betulinic acid is one of the active constituents derived from traditional Chinese medicine. The inhibitory effect of betulinic acid on tumour growth has been highlighted, yet research on its effect on HCC remains scanty. In this study, we aimed to systematically explore the anti-neoplastic action of betulinic acid in HCC and the role of metastasis-associated lung adenocarcinoma transcript 1 (MALAT1) in betulinic acid-induced tumour regression. Long non-coding RNA MALAT1 is identified as an oncogenic factor. First, we measured the in vivo effect of betulinic acid by establishing an orthotopic HCC implantation model. We observed no specific toxicity, but the deceleration of orthotopic HCC tumour growth in immunocompromised mice was observed. The in vitro action of betulinic acid was subsequently examined using HCC cells. We observed the inhibition of betulinic acid on HCC cellular functions, including cell cycle arrest, decreased cell proliferation, attenuated colony formation ability, and mitigated migration and invasion capacity. The effect was accompanied by the reduced accumulation of autophagosomes and the enhanced conversion from LC3-I to LC3-II, as well as the reduced expression of inhibitors of apoptosis proteins (IAPs). Also, a decline in the expression of MALAT1 was observed in betulinic acid-intervened models, followed by an elevation in the level of miR-22-3p and decrease in the level of XIAP. Thereafter, the implication of MALAT1 in HCC progression was explored in-depth. First, our findings postulated that MALAT1 induced the upregulation of metastasis-related molecules including ICAM1, as well as the overexpression of CREB, a crucial transcriptional factor for tumour progression. In addition, MALAT1 phenotypically and functionally activated the TNF signalling pathway. The further co-intervention of the TNF pathway inhibitor in MALAT1-pre-treated models attenuated the progression and metastasis of HCC cells and malignancy nodules in mice, with the phenotypical evidence of decreased ICAM1 and CREB levels. Finally, we sought to illustrate the mechanism of betulinic acid-induced MALAT1 regulation. Betulinic acid intervention induced observable inhibition of MALAT1-induced XIAP upregulation through the reactivation of miR-22-3p. Surprisingly, the presence of betulinic acid induced no significant inhibition of MALAT1-mediated CREB activation. In summary, this study underscores the pivotal role of MALAT1-mediated tumour progression in HCC. MALAT1 mediated the apoptotic pathway by sponging miR-22-3p. On the other hand, MALAT1 activated the TNF signalling pathway and thereafter upregulated the expression of CREB. Meanwhile, the inhibition of HCC growth by betulinic acid was identified to rely on the MALAT1-involved activation of miR-22-3p and the downstream XIAP regression. The findings demonstrate new mechanisms of action underlying MALAT1-mediated HCC progression, and propose a novel apoptosis-promoting drug candidate for HCC management. Our study sheds light on the therapeutic opportunities from herbal medicine for HCC treatment.