MYC (v-myelocytomatosis viral oncogene homologue) is a regulator gene that encodes for a nuclear phosphoprotein. Porcine MYC gene was mapped on chromosome SSC 4p13 and is associated with a variety of functions such as cell proliferation and cell growth. MYC expression is coupled to a multitude of physiological processes and is regulated by hormones, growth factors, cytokines, lymphokines, nutritional status, development and differentiation. MYC is also involved in myogenesis, muscle hyperplasia and adipogenesis. In this study, we investigated SNPs in MYC gene and their association with economic traits in Duroc, Landrace and Yorkshire populations. We detected a single point mutation in exon 3 of porcine MYC gene as a change of T to C at 906 base (amino acid position 302, nonsynomous mutation of alanine) in MYC-N domain. MYC mutation (T906C) was significantly associated with age at 90 kg in these breeds, signifying that this mutation can serve as a selection marker for growth traits in pigs.

In this study, we elucidated the molecular mechanism of silymarin by which silymarin may inhibits cell proliferation in human colorectal cancer cells in order to search the new potential anti-cancer target associated with the cell growth arrest. Silymarin reduced the level of c-Myc protein but not mRNA level indicating that silymarin-mediated downregulation of c-Myc may result from the proteasomal degradation. In the confirmation of silymarin-mediated c-Myc degradation, MG132 as a proteasome inhibitor attenuated c-Myc degradation by silymarin. In addition, silymarin phosphorylated the threonine-58 (Thr58) of c-Myc and the point mutation of Thr58 to alanine blocked its degradation by silymarin, which indicates that Thr58 phosphorylation may be an important modification for silymarin-mediated c-Myc degradation. We observed that the inhibition of ERK1/2, p38 and GSK3β blocked the Thr58 phosphorylation and subsequent c-Myc degradation by silymarin. Finally, the point mutation of Thr58 to alanine attenuated silymarin-mediated inhibition of the cell growth. The results suggest that silymarin induces the cell growth arrest through c-Myc proteasomal degradation via ERK1/2, p38 and GSK3β-dependent Thr58 phosphorylation.

The four transcription factors Oct4, Sox2, Klf4 and c-Myc have been used for making induced pluripotent stem cells. Many efforts have focused on reducing the number of transcription factors, especially c-Myc and Klf4 known as oncogene, for making induced pluripotent stem cells. Recently it have been demonstrated that Oct4 and Sox2 are able to reprogram human fibroblasts or cord blood cells to induced pluripotent stem cells and Oct4 has the ability to reprogram mouse and human neural stem cell to induced pluripotent stem cells. These researches imply cell types for reprogramming experiments have great influence on selection of reprogramming factors. Here we report that pig kidney cortex fibroblasts need only c-Myc factor when they are used for making induced pluripotent stem cells. We used two vector system including drug-inducible vector system and constitutive expression vector system. The two systems generate induced pluripotent stem cells from pig kidney fibroblasts successfully. These one-factor induced pluripotent stem cells are not only similar but also different to pig embryonic stem-like cells. These two one-factor induced pluripotent stem cell lines can express pluripotency related genes and be differentiated into all three germ layers in vitro. However, these two cell lines can be sub-cultured as a single cell by trypsin. Our results support that single factor, c-Myc, is sufficient to converting pig kidney cortex fibroblasts into induced pluripotent stem cells.