Expression of functional human STK11 protein in Escherichia coli

STK11(serine/threonine kinase 11), a multi-functional protein reported recently, possibly participates in a broad range of cellular processes, including regulation of cell cycle, p53-mediated apoptosis, ras-induced cell transformation and cell polarization. An efficient expression of functional STK11 in Escherichia coli will promote the study on its structure and function. Inducible prokaryotic expression vector pET-Nus-STK11(with Nus fusion tag) was constructed with pET-44a(+) and the cDNA of STK11 gene cloned in our lab. pET-Nus-STK11 was then expressed in both BL21(DE3) and Rosetta-gami (DE3)pLysS on the induction of IPTG. SDS-PAGE and Western blot indicated that recombinant Nus-STK11 obtained in BL21(DE3) was in the form of inclusion body, whereas that from Rosetta-gami (DE3)pLysS was mainly in soluble fraction, and accounted for 8.9% and 16.7% of the total protein, respectively. After purification and refolding, the obtained recombinant protein was carried into SMMC-7721 cells by Chariot to observe its influence on cell growth and cell cycle. Nus-STK11 from BL21(DE3) was proved to be lack of any tumor-suppression activity, while a growth inhibitory ratio of 47.05% on SMMC-7721 cell was observed, and cell cycle progression of SMMC-7721 cells was also arrested from G_0/G_1 to S phase, with the Nus-STK11 from Rosetta-gami (DE3)pLysS, indicating that the above recombinant fusion protein from Rosetta-gami (DE3)pLysS had significant biological activity. This is the first report on functional recombinant STK11 protein expressed in Escherichia coli.