SKP2 and small cell lung carcinoma: The different performances of MLN4924 in primary mouse SCLC lung cell and primary mouse SCLC liver metastatic cell, implied that some important mechanisms might change during SCLC cell metastasis, and this mechanism changes might relate to neddylation-dependent activities of MLN4924, indicating that SCFSkp2 or other E3 neddylation might promote the SCLC cell metastasis, other than only Skp2 protein or the ubiquitination mediate by Skp2.