RAB37 multiple alleles, transcription activation and evolution in mammals

Rab37 mediates trafficking and membrane presentation of PD-1 to sustain T cell exhaustion in lung cancer

BACKGROUND

Programmed cell death protein 1 (PD-1) is an immune checkpoint receptor expressed on the surface of T cells. High expression of PD-1 leads to T-cell dysfunction in the tumor microenvironment (TME). However, the mechanism of intracellular trafficking and plasma membrane presentation of PD-1 remains unclear.

METHODS

Multiple databases of lung cancer patients were integratively analyzed to screen Rab proteins and potential immune-related signaling pathways. Imaging and various biochemical assays were performed in Jurkat T cells, splenocytes, and human peripheral blood mononuclear cells (PBMCs). Rab37 knockout mice and specimens of lung cancer patients were used to validate the concept.

RESULTS

Here, we identify novel mechanisms of intracellular trafficking and plasma membrane presentation of PD-1 mediated by Rab37 small GTPase to sustain T cell exhaustion, thereby leading to poor patient outcome. PD-1 colocalized with Rab37-specific vesicles of T cells in a GTP-dependent manner whereby Rab37 mediated dynamic trafficking and membrane presentation of PD-1. However, glycosylation mutant PD-1 delayed cargo recruitment to the Rab37 vesicles, thus stalling membrane presentation. Notably, T cell proliferation and activity were upregulated in tumor-infiltrating T cells from the tumor-bearing Rab37 knockout mice compared to those from wild type. Clinically, the multiplex immunofluorescence-immunohistochemical assay indicated that patients with high Rab37+/PD-1+/TIM3+/CD8+ tumor infiltrating T cell profile correlated with advanced tumor stages and poor overall survival. Moreover, human PBMCs from patients demonstrated high expression of Rab37, which positively correlated with elevated levels of PD-1+ and TIM3+ in CD8+ T cells exhibiting reduced tumoricidal activity.

CONCLUSIONS

Our results provide the first evidence that Rab37 small GTPase mediates trafficking and membrane presentation of PD-1 to sustain T cell exhaustion, and the tumor promoting function of Rab37/PD-1 axis in T cells of TME in lung cancer. The expression profile of Rab37high/PD-1high/TIM3high in tumor-infiltrating CD8+ T cells is a biomarker for poor prognosis in lung cancer patients.

Germline stem cells in human

The germline cells are essential for the propagation of human beings, thus essential for the survival of mankind. The germline stem cells, as a unique cell type, generate various states of germ stem cells and then differentiate into specialized cells, spermatozoa and ova, for producing offspring, while self-renew to generate more stem cells. Abnormal development of germline stem cells often causes severe diseases in humans, including infertility and cancer. Primordial germ cells (PGCs) first emerge during early embryonic development, migrate into the gentile ridge, and then join in the formation of gonads. In males, they differentiate into spermatogonial stem cells, which give rise to spermatozoa via meiosis from the onset of puberty, while in females, the female germline stem cells (FGSCs) retain stemness in the ovary and initiate meiosis to generate oocytes. Primordial germ cell-like cells (PGCLCs) can be induced in vitro from embryonic stem cells or induced pluripotent stem cells. In this review, we focus on current advances in these embryonic and adult germline stem cells, and the induced PGCLCs in humans, provide an overview of molecular mechanisms underlying the development and differentiation of the germline stem cells and outline their physiological functions, pathological implications, and clinical applications.