RAC2 promotes abnormal proliferation of quiescent cells by enhanced JUNB expression via the MAL-SRF pathway.

Radiation-induced lung injury (RILI) occurs most often in radiotherapy of lung cancer, esophageal cancer, and other thoracic cancers. The occurrence of RILI is a complex process that includes a variety of cellular and molecular interactions, which ultimately result in carcinogenesis. However, the underlying mechanism is unknown. Here we show that Ras-related C3 botulinum toxin substrate 2 (RAC2) and transcription factor jun-B (JUNB) were upregulated in non-small cell carcinoma (NSCLC) tissues and were associated with poor prognoses for NSCLC patients. Ionizing radiation also caused increased expression of RAC2 in quiescent stage cells, and the reentry of quiescent cells into a new cell cycle. The activity of the serum response factor (SRF) was activated by RAC2 and other Rho family genes (RhoA, ROCK, and LIM kinase). Consequently, JUNB acted as an oncogene and induced abnormal proliferation of quiescent cells. Together, the results showed that RAC2 can be used as a target gene for radiation protection. A better understanding of the RAC2 and JUNB mechanisms in the molecular etiology of lung cancer will be helpful in reducing cancer risks and side effects during treatment of this disorder. Our study therefore provides a new perspective on the involvement of RAC2 and JUNB as oncogenes in the tumorigenesis of NSCLC.

[Expression of TPO mimetic peptide chimeric proteins with human IgG1 Fc fragments and their biological characters].

Many antineoplastic agents can cause myelosuppression and thrombocytopenia. Thrombopoietin (TPO) is believed to be the major cytokine affecting the proliferation and maturation of megakaryocytes and increasing circulating platelet levels. We have designed and synthesized a TPO mimetic peptide, it can increase circulating platelet levels in vivo. For increasing half-life and forming dimer, the peptide was expressed as chimeric proteins with human IgG1 Fc fragments. The cDNA of TPO mimetic peptide was synthesized chemically and linked respectively to 5' terminus of human IgG1 Fc cDNA fragments in various length (Fc1: Fc 5' 648 bp; Fc2: Fc 5' 270 bp; Fc3: Fc 5' 267 bp; Fc4: Fc 5' 90 bp), and cloned into expression plasmid pET28a (+) for constructing four recombinant plasmids. By transforming the four recombinant plasmids into E. coli. BL21 (DE3) respectively, we got 3 kinds of engineered E. coli which express TPO + Fc chimeric proteins(28 kD TPO + Fc1, 12 kD TPO + Fc2 and 12 kD TPO + Fc3) at high level respectively, the expressed proteins were purified with DEAE-Sepharose FF and S-Sepharose FF column. The bioactivities of the expressed chimeric proteins(TPO + Fc1, TPO + Fc2 and TPO + Fc3), TPO mimetic peptide, and PEG4000 coupled TPO mimetic peptide were evaluated with Ba/F3-mp1 in vitro and with carboplatin-induced thrombocytopenia mice in vivo, the expressed chimeric proteins have higher activity than TPO mimetic peptide both in vitro and in vivo, the EC50 on Ba/F3-mp1 cells were 13, 10, 10, 50, and 25 nmol/L respectively, all of them can increase circulating platelet counts. Their imol/Lunogenicity were valuated in mice, none of them can elicit mice to produce antibodies to TPO mimetic peptide, meanwhile three TPO + Fc chimeric proteins can elicit mice to produce antibodies to human IgG1 Fc. These studies have laid basis for production of TPO mimetic peptide by genetic engineering.