Small proline-rich repeat protein 3 enhances the sensitivity of esophageal cancer cells in response to DNA damage-induced apoptosis

Small proline-rich repeat protein 3 (SPRR3) has been linked with the altered chemoradiosensitivity, however the underlying molecular mechanisms remain elusive. Here, we report that ectopic overexpression of SPRR3 enhanced the sensitivity of cells in response to DNA damage-induced apoptosis via loss of mitochondrial membrane potential (MMP), and increasing activation of caspase 3 in human esophageal cancer cell lines. Conversely, siRNA knockdown of SPRR3 reduced apoptosis. We found that SPRR3 was localized in mitochondria and interacted with Bcl-2 in vivo, thus facilitating Bax mitochondrial translocation and the subsequent release of cytochrome c, and thereby enhancing cell sensitivity to DNA damage stimuli. In clinical samples, expression of SPRR3 was associated with the pathologic response (P = 0.007 in radiotherapy group, P = 0.035 in preoperative radiotherapy group) and good survival of patients with locally advanced esophageal squamous cell carcinoma (ESCC, P = 0.008). Taken together, our results implicate that SPRR3 might serve as a radiation-sensitive predictor of ESCC.