Adrenocortical Suicide Gene CYP4B1 Promotes Adrenocortical Carcinoma Cell Death by Dysregulating the TNF Signaling Pathway
*Norman G. Nicolson, Glenda G. Callender, *Courtney E. Gibson, *Reju Korah, Tobias Carling
Yale School of Medicine, Department of Surgery, New Haven, CT
Objective: Re-expression of cytochrome P450 4B1 (CYP4B1) induces loss of viability in adrenocortical carcinoma (ACC) cells. The mechanism of CYP4B1-promoted cell death remains elusive, limiting its utility as a therapeutic target. Using targeted gene-expression arrays, we sought to isolate the cell-death pathways undermined by CYP4B1 suppression in ACC.
Design: Gene expression analyses of patient adrenocortical tumor tissues and established ACC cell lines
Setting: Tertiary academic center
Patients (or Other Participants): Ten ACCs, twelve adrenocortical adenomas (ACAs), and two ACC cell lines
Interventions: Established ACC cell lines were manipulated for transient ectopic expression of CYP4B1 gene. The CYP4B1-transfected cells were non-viable but were subjected to gene expression arrays to identify components of the cell-death pathways involved. The candidate genes were validated in tumor and normal adrenal tissues using quantitative PCR.
Main Outcome Measures: Gene expression profiling of cell-death pathways in ACC
Results: ACC cells undergoing loss of viability consequent to CYP4B1 re-expression showed upregulation of TNF-alpha signaling receptor TNFRSF1A and multiple other activators of apoptosis including BAD, BIK, and the BCL2 antagonist BAX. The gene expression profiles of each cell line were distinct, likely reflecting different pathways of cell death at play. Expression analysis of selected TNF-α candidate genes in patient samples revealed reduced expression of TNFRSF1A in ACC relative to ACA (p= 0.047), while FADD was over-expressed in both ACA and ACC (p= 0.03 and 0.002 respectively) relative to normal adrenal.
Conclusions: Although ACCs exhibit loss of CYP4B1 expression, the mechanism through which suppression of this suicide gene might contribute to tumorigenesis has not been described. Our study suggests dysregulation of TNF-alpha signaling as a potential mechanism of CYP4B1-suicide signaling in ACC.