Proteomic Identification of DNA-PK Involvement within the RET Signaling Pathway

Abstract

Constitutive activation of the Rearranged during Transfection (RET) proto-oncogene leads to the development of MEN2A medullary thyroid cancer (MTC). The relatively clear genotype/phenotype relationship seen with RET mutations and the development of MEN2A is unusual in the fact that a single gene activity can drive the progression towards metastatic disease. Despite knowing the oncogene responsible for MEN2A, MTC, like most tumors of neural crest origin, remains largely resistant to chemotherapy. Constitutive activation of RET in a SK-N-MC cell line model reduces cell sensitivity to chemotherapy. In an attempt to identify components of the machinery responsible for the observed RET induced chemoresistance, we performed a proteomic screen of histones and associated proteins in cells with a constitutively active RET signaling pathway. The proteomic approach identified DNA-PKcs, a DNA damage response protein, as a target of the RET signaling pathway. Active DNA-PKcs, which is phosphorylated at site serine 2056 and localized to chromatin, was elevated within our model. Treatment with the RET inhibitor RPI-1 significantly reduced s2056 phosphorylation in RET cells as well as in a human medullary thyroid cancer cell line. Additionally, inhibition of DNA-PKcs activity diminished the chemoresistance observed in both cell lines. Importantly, we show that activated DNA-PKcs is elevated in medullary thyroid tumor samples and that expression correlates with expression of RET in thyroid tumors. These results highlight one mechanism by which RET signaling likely primes cells for rapid response to DNA damage and suggests DNA-PKcs as an additional target in MTC.

PRKDC regulates chemosensitivity and is a potential prognostic and predictive marker of response to adjuvant chemotherapy in breast cancer patients

“…The potential mechanism by which PRKDC regulates metastasis is through mediation of transcriptional network or through regulation of secreted proteins involved in migration and invasion (24,25). Due to its role in mediating DDR, aberrant expression/ activation of PRKDC has been associated with chemo-or radio-resistance (26,27). A previous study showed that PRKDC regulated AKT activation and inhibited apoptosis in ovarian cancer cells with acquired platinum resistance (28,29).…”

Current status of the prognostic molecular markers in medullary thyroid carcinoma

“…To date, there are only a few reports devoted to an extensive proteomic scale analysis in MTC. Similarly to the whole transcriptome analysis, proteomic studies are focused on the biology of MTC ( 78 , 79 , 80 , 81 ). The recently published proteomic analysis involved three sporadic MTC tumors and corresponding normal tissue ( 82 ).…”