An adrenocortical carcinoma (ACC) arises from the adrenal gland on the superior aspect of the kidney. Although ACCs are relatively rare, they carry a very poor prognosis. In fact, the five-year survival rate is as low as 20–45%, due largely to delays in diagnosis.1 Many adrenal gland tumors detected are adrenocortical adenomas (ACAs), a type of benign tumor (as opposed to an ACC). Unfortunately, malignancy is determined first by the size of the tumor and secondly through surgery. This leads to unnecessary abdominal surgery; alternatively, it may allow the tumor sufficient time to grow further and to metastasize. Improved diagnostics for ACC may lead to better health outcomes for both these categories of patients.
A recent study by Kjellin et al. aimed to gain insight into the molecular pathology of ACCs.2 They successfully used proteomic studies to identify groups of proteins that are differentially expressed in ACAs and ACCs.
The investigators fractionated the whole cell lysate from excised human tumor tissue and enriched for the microsomal protein fraction; they performed the enrichment process to increase the likelihood of differentiation between low-abundance proteins. Kjellin et al. homogenized the microsomes by crushing patient samples with 1 ml 0.1 M potassium phosphate buffer, pH 7.4, 0.25 M sucrose and protease inhibitors. They then applied a multistep centrifugation and incubation process to distill the microsomal pellets. Following this, they used tryptic digestion and iTRAQ labeling to quantify the proteins within each sample, before performing LC-MS/MS on a hybrid LTQ Orbitrap Velos mass spectrometer (Thermo Scientific) to identify the proteins. MS spectra were searched using Sequest combined with the Percolator algorithm (version 2.0) for peptide-spectrum-match search optimization using Proteome Discoverer software version 1.3 (Thermo Scientific). The researchers used ProteinCenter software version 3.10.10004 (Thermo Scientific) to perform an enrichment analysis.
Across all 14 patient samples, researchers were able to accurately quantify 1,902 proteins. They used orthogonal projections to latent structures (OPLS) and t-test analysis to identify characteristic proteins that could differentiate between ACAs and ACCs. In doing so, they found 26 proteins identified as up- or down-regulated. Kjellin et al. found that 14 of the proteins identified were involved in mitochondrial dysfunction and were down-regulated. Additionally, insulin-like growth factor 2 (IGF2) was elevated in ACC and there was a two-fold difference in GRIM-19 expression between ACA and ACC. In other studies, investigators have shown that GRIM-19 interacts with STAT3 and plays a role in biological responses such as cell growth and apoptosis. Aldolase A, a glycolytic enzyme, was also up-regulated.
Taken together, these findings suggest that in ACC tumorigenesis, changes take place in the mitochondrial proteome that are distinct from the changes in ACA masses. Additionally, the findings indicate an increase in ACC glycolysis rate as compared to ACA. Understanding the pathophysiology of these types of tumors may lead researchers to find biomarkers that could be used to improve diagnostics down the track.
1. Stephan, E.A., et al. (2008) “Adrenocortical carcinoma survival rates correlated to genomic copy number variants,” Journal of Molecular Cancer Therapeutics, 7(2) (pp. 425–31).
2. Kjellin, H., et al. (2014) “Differentially Expressed Proteins in Malignant and Benign Adrenocortical Tumors,” PLOS ONE, 9(2), doi: 10.1371/journal.pone.0087951.
Post Author: Miriam Pollak. Miriam specialised in neuroscience as an undergraduate but traded in lab work for a post graduate degree in science communication.
She has since had a career that has spanned science communication, science education and communications management.
However, Miriam has found her bliss balancing her love of writing and disseminating medical research with managing a multimillion dollar research budget for a childhood cancer charity in Australia.