Autophagy-related gene 12 (ATG12) is a novel determinant of primary resistance to HER2-targeted therapies: Utility of transcriptome analysis of the autophagy interactome to guide breast cancer treatment

Abstract

The autophagic process, which can facilitate breast cancer resistance to endocrine, cytotoxic, and molecularly targeted agents, is mainly regulated at the post-translational level. Although recent studies have suggested a possible transcriptome regulation of the autophagic genes, little is known about either the analysis tools that can be applied or the functional importance of putative candidate genes emerging from autophagy-dedicated transcriptome studies. In this context, we evaluated whether the constitutive activation of the autophagy machinery, as revealed by a transcriptome analysis using an autophagy-focused polymerase chain reaction (PCR) array, might allow for the identification of novel autophagy-specific biomarkers for intrinsic (primary) resistance to HER2-targeted therapies. Quantitative real-time PCR (qRT-PCR)-based profiling of 84 genes involved in autophagy revealed that, when compared to trastuzumab-sensitive SKBR3 cells, the positive regulator of autophagic vesicle formation ATG12 (autophagy-related gene 12) was the most differentially up-regulated gene in JIMT1 cells, a model of intrinsic cross-resistance to trastuzumab and other HER1/2-targeting drugs. An analysis of the transcriptional status of ATG12 in > 50 breast cancer cell lines suggested that the ATG12 transcript is commonly upregulated in trastuzumab-unresponsive HER2-overexpressing breast cancer cells. A lentiviral-delivered small hairpin RNA stable knockdown of the ATG12 gene fully suppressed the refractoriness of JIMT1 cells to trastuzumab, erlotinib, gefitinib, and lapatinib in vitro. ATG12 silencing significantly reduced JIMT1 tumor growth induced by subcutaneous injection in nude mice. Remarkably, the outgrowth of trastuzumab-unresponsive tumors was prevented completely when trastuzumab treatment was administered in an ATG12-silenced genetic background. We demonstrate for the first time the usefulness of low-density, autophagy-dedicated qRT-PCR-based platforms for monitoring primary resistance to HER2-targeted therapies by transcriptionally screening the autophagy interactome. The degree of predictive accuracy warrants further investigation in the clinical situation.

Acquired resistance to metformin in breast cancer cells triggers transcriptome reprogramming toward a degradome-related metastatic stem-like profile

“…[7][8][9][10][11][12][13][14][15][16][17][18][19]101 Although the demonstration of resistance to oncogenemediated targeted therapy through the adaptation of cellular metabolism suggests that the rewiring of cellular metabolism plays a fundamental, convergent role for oncogenes and signal transduction in promoting tumorigenesis, little is known about how the cancer signaling networks are remodeled and which pathways are invoked to sustain survival in the presence of drugs targeting central key signaling metabolic hubs (e.g., AMPK, mTOR) that respond to an array of signaling metabolic inputs and regulate a range of downstream effector metabolic pathways. Together, our current findings suggest, for the first time, that chronic adaptation to high doses of the AMPK agonist/mTOR inhibitor metformin appears to causally involve 2 highly intertwined molecular phenomena underlying enhanced cancer aggressiveness.…”

“…[7][8][9][10][11][12][13][14][15][16][17][18][19] While it might appear intuitive that deregulated cancer metabolism can activate pro-survival signaling and decrease druginduced apoptosis to provide a general, unspecific protection against cell injuries induced by multiple types of cytotoxicities, it is worth noting that resistance to oncogene-mediated targeted therapy has been shown to require a shift toward the very same metabolic state that is controlled by growth factor signaling. 20,21 In cancer cells sensitive to lapatinib, the small-molecule dual inhibitor of the oncogenes EGFR and HER2, receptor tyrosine kinase signaling is disrupted, and activity of its Ras, PI3K, and mTOR downstream effectors is abrogated; because oncogenedependent metabolic rewiring is prevented, cancer cell death is observed.…”

Potentially Functional Variants of ATG16L2 Predict Radiation Pneumonitis and Outcomes in Patients with Non–Small Cell Lung Cancer after Definitive Radiotherapy

“…20 More recently, ATG12 silencing was shown to significantly reduce breast cancer cell growth in nude mice, which suggests that ATG12 may be an oncogenic protein. 21 …”

STAT3 down regulates LC3 to inhibit autophagy and pancreatic cancer cell growth

“…Therefore autophagy contributes to cellular homeostasis by removing damaged organelles and maintaining their normal turnover[4, 5]. The role of autophagy in carcinogenesis is complex with reports demonstrating functions in tumor promotion and suppression as well as a contribution to therapeutic resistance[6-8]. For example, curcumin suppresses malignant glioma growth through autophagy induction[9].…”