Tauroursodeoxycholic acid mediates endoplasmic reticulum stress and autophagy in adrenocortical carcinoma cells

What is the role of CHCHD2 in adrenal tumourigenesis?

PURPOSE

CHCHD2 is an antiapoptotic mitochondrial protein acting through the BCL2/BAX pathway in various cancers. However, data on the regulatory role of CHCHD2 in adrenal tumourigenesis are scarce.

METHODS

We studied the expression of CHCHD2, BCL2, and BAX in human adrenocortical tissues and SW13 cells. mRNA and protein levels were analyzed through qPCR and immunoblotting, respectively, in 16 benign adrenocortical neoplasms (BANs), along with their adjacent normal adrenal tissues (controls), and 10 adrenocortical carcinomas (ACCs). BCL2/BAX mRNA expression was also analyzed in SW13 cells after CHCHD2 silencing. MTS, flow cytometry and scratch assays were performed to assess cell viability, apoptosis, and invasion, respectively.

RESULTS

BCL2 and CHCHCD2 mRNA and protein expression was increased in BANs compared to normal adrenal tissues whereas BAX was decreased. BAX and CHCHD2 mRNA and protein levels were significantly downregulated and upregulated, respectively, in ACCs compared with either BANs or controls. Expression of the studied genes was not different among cortisol-secreting and nonfunctional ACAs. No significant association was found between genes' expression and other established prognostic markers of ACCs patients. In vitro analysis showed that CHCHD2 silencing resulted in reduced cell viability and invasion as well as increased SW13 cells apoptosis.

CONCLUSIONS

CHCHD2 expression seems to be implicated in adrenal tumourigenesis and its absence resulted to increased apoptosis in vitro. However, the exact mechanism of action and particularly its association with the BAX/BCL2 pathway needs to be further studied and evaluate whether it could be a protentional therapeutic target.

Modulation of Autophagy in Adrenal Tumors

Adrenal masses are one of the most common tumors in humans. The majority are benign and non-functioning and therefore do not require immediate treatment. In contrast, the rare adrenal malignant tumors are often highly aggressive and with poor prognosis. Besides usually being detected in advanced stages, often already with metastases, one of the reasons of the unfavorable outcome of the patients with adrenal cancer is the absence of effective treatments. Autophagy is one of the intracellular pathways targeted by several classes of chemotherapeutics. Mitotane, the most commonly used drug for the treatment of adrenocortical carcinoma, was recently shown to also modulate autophagy. Autophagy is a continuous programmed cellular process which culminates with the degradation of cellular organelles and proteins. However, being a dynamic mechanism, understanding the autophagic flux can be highly complex. The role of autophagy in cancer has been described paradoxically: initially described as a tumor pro-survival mechanism, different studies have been showing that it may result in other outcomes, namely in tumor cell death. In adrenal tumors, this dual role of autophagy has also been addressed in recent years. Studies reported both induction and inhibition of autophagy as a treatment strategy of adrenal malignancies. Importantly, most of these studies were performed using cell lines. Consequently clinical studies are still required. In this review, we describe what is known about the role of autophagy modulation in treatment of adrenal tumors. We will also highlight the aspects that need further evaluation to understand the paradoxical role of autophagy in adrenal tumors.