支原体保守多肽SGLP通过Rac1和Rab7协同激活Stat3促进乳腺肿瘤发生的作用和机制

Mycoplasma genus comprises a special group of microbes that cause persistent infection in mammals, which can induce malignant transformation of host cells. However, the molecular basis of mechanisms by which mycoplasma promotes tumorigenesis are largely unknown. In previous study, we identified a mycoplasmal conserved small GTPase-like polypeptide (SGLP) which can promote proliferation of human cancer cells in vitro. We found that SGLP can activate small GTPase Rac1, through which it can activate Stat3; and that the effect is dependent on the N-terminal WxxxE motif-containing domain of SGLP. We also found that SGLP can subvert the function of small GTPase Rab7, which is condusive to phosphorylation of Stat3. Therefore, we hypothesize that the WxxxE motif-containing SGLP interacts with small GTPases Rac1 and Rab7 synergistically, through which SGLP may activate Stat3, promoting tumorigenesis. To confirm the hypothesis, we aim to investigate the effect of SGLP on mammary epithelial malignant transformation in vitro and in vivo, and to prove that SGLP promotes mammary epithelial malignant transformation by activating Rac1 and inhibiting Rab7 synergistically. This study will provide new insights into the etiologic, therapeutic and prophylactic aspects of breast cancer, which is of an important clinical significance.

支原体是一类特殊的原核生物，长期支原体感染可导致细胞恶性转化，但是其具体的分子机制尚不清楚。我们前期研究发现了一个保守的支原体小GTP结合蛋白类似多肽（SGLP）具有促进肿瘤细胞增殖的作用。进一步研究表明，SGLP可通过宿主小GTP结合蛋白Rac1激活Stat3，而此作用依赖于SGLP的N端含有WxxxE基序的结构域。我们还发现SGLP可影响小GTP结合蛋白Rab7的功能，从而促进Stat3磷酸化。因此我们推测，含WxxxE基序的SGLP保守多肽通过Rac1和Rab7途径协同激活 Stat3 活性进而促进肿瘤发生。为证实上述假设，本项目拟在细胞和整体水平研究SGLP对乳腺上皮细胞恶性转化的作用，阐明SGLP通过激活Rac1和抑制Rab7协同促进人乳腺上皮细胞恶性转化的机制。本研究将为乳腺肿瘤病因及防治提供新的认识，具有重要的临床意义。

本项目在前期发现的基础上继续研究支原体蛋白片段SGLP对人乳腺肿瘤细胞小GTP蛋白的影响和其中的机制。通过实验我们发现，乳腺癌组织中可检测出支原体核酸片段，支原体感染与乳腺癌具有相关性；支原体保守蛋白片段SGLP的N端多肽对宿主乳腺肿瘤细胞具有抑制恶性转化作用，其N端含WXXXE基序的多肽通过抑制小GTP蛋白RAC1进而抑制STAT3和ERK/GSK3β通路发挥抗肿瘤作用；支原体污染增加人肿瘤细胞外泌体生成并改变其小RNA表达模式；SGLP蛋白片段的编码WVLGE基序的RNA可被宿主细胞处理为外源性miRNA，这种外源性miRNA可靶向宿主YAP1基因3‘UTR，YAP1的下调进而导致miRNA表达模式的转换；表达模式改变的miRNA子集包括可靶向小GTP蛋白RAC1, CDC42, RHOA,以及RAB5的miRNA。上述结果发现了SGLP衍生的抗肿瘤肽段，发现了SGLP的编码RNA衍生的外源性miRNA通过靶向YAP1改变宿主内源性miRNA生成模式，继而影响小GTP蛋白分子开关网络的机制。可依此开发出抗肿瘤的多肽，并开发出调控宿主小GTP网络的小RNA类似物。