We are grateful to Prof. Carlos López-Otín and Prof.Takako Sasaki for providing us cell lines and reagents. This work was supported by a grant from the Instituto de Salud Carlos III (Spain) (FISS PI11/00371) and Fondos FEDER to S. Cal and partially supported by a grant from the Ficyt (Asturias) (Grupin 14/069) to S. Cal, A.J. Obaya, José A Vega and Marcos Pérez Basterrechea; and Plan Nacional de I+D+I 2013-2016 ISCIII (PI13/00259) and CIBERONC to J.M. García-Pedrero. T. Fontanil and Y. Mohamedi are recipients of a fellowship from the Instituto Universitario de Oncología, and from the Ficyt respectively. The Instituto Universitario de Oncología is supported by Fundación Bancaria Caja de Ahorros de Asturias-IUOPA.