The Impact Of Liver Kinase B1(LKB1) On Dendritic Cell Functions And Mechanisms

Liver kinase B1(LKB1)is a serine threonine kinase that regulates cell growth,development and metabolism.The gene for LKB1 is a tumor suppressor gene,and abnormal LKB1 has been found in various malignant tumors of digestive tract and lung cancer.At present,more and more studies have shown that LKB1 plays an important role in tumor immunity,suggesting that LKB 1 plays a pivotal role in immune responses.Dendritic cells(DCs),as the initiator of immune response,as well as connector of both innate and adaptive immunity,are important cell type in monitoring tumor growth and mutation.However,due to the scarcity of DCs in vivo and the difficulty of their separation,the role of LKB1 in DC has been poorly understood.To this end,this Master’s project used advanced lentivirus plasmid system to knock down or overexpress LKB1 gene to obtain a stable DC line DC 2.4 with either loss-of-LKB1 function,or gain-of-LKB1 function respectively,before comprehensive characterization of their biological function was performed.We found that the LKB1 in DCs does not affect their phagocytosis and cross-presentation of antigens to CD8+T cells,but can increase their ability to stimulate the proliferation of CD4+ T cells,because the number of proliferated CD4+T cells significantly increased in the mixed lymphocyte reaction(MLR)with DCs overexpressed LKB1,whereas adoptive transfer of LKB 1 knockeddown DCs to the mice suppressed the number of splenic CD4+T cells to enter proliferating cycles.With regard to the impact of LKB1 in DCs on T cell differentiation,we found that it mainly affected the regulatory T cells(Treg)subset,as adoptive transfer of LKB 1-overexpressing DCs significantly reduced the percentage of Treg in spleen,while opposite outcomes occurs when LKB1-knocked-down DCs were administrated.Further exploration of the molecular mechanisms of these phenotypes revealed that LKB1 inhibited the expression of OX40L,a tumor necrosis factor superfamily member that stimulates Treg proliferation,and upregulated immune inhibitive cytokine IL-10.In terms of its effect on the function of CD8+T cells in vivo,we found that the injection of DC with the loss-of-LKB1 function into mice could reduce the production of granzyme and perforin,indicating compromised tumor killing cability and favorable tumor growth environment.Collectively,these data suggest that LKB1 in DC,on the one hand,promotes the proliferation but inhibits the differentiation of CD4+T cells towards Treg,thus maintaining host at a relatively stronger immune response status.On the other hand,LKB 1 ensures tumor killing by keeping normal DC-mediated CD8+T cell function.These two hands work together to enhance the host anti-tumor ability.These findings explain the immune suppressive mechanism of LKB1 in DCs,which can provide a theoretical basis for the development of therapeutic drugs to treat tumors and their related immunological diseases.