Deciphering the divergent roles of phosphatases in PD-1 and cytokine signaling
Blockade of inhibitory receptor (IR) signaling has recently revolutionized cancer treatments, enabling reactivation of tumor-specific T cell responses with remarkable clinical benefit. IRs contribute to T cell dysfunction by interfering with activating cascades such as Akt and ERK (extracellular signal-regulated kinase). In T cells, but also in natural killer (NK) cells, the phosphatase SHP-2 (SH2 domain-containing protein tyrosine phosphatase-2) is a major cytoplasmic interactor and has been proposed to mediate the effects of IRs. However, the best-known function of SHP-2 is to activate the ERK pathway in response to hormones and growth factors in various cell types, through a mechanism that remains debated. As a consequence, SHP-2 is considered a proto-oncogene and recently developed inhibitors have shown promise in treating multiple cancers. The function of SHP-2 in immune cells remains therefore unclear, urging investigations on its physiological relevance and the underlying molecular mechanisms. We recently observed that Shp-2 deficiency in NK cells, which mediate antiviral and anticancer immunity, does not cause overt defects associated with IR signaling. However, we found that Shp-2 is essential for ERK engagement and for NK cell expansion in response to interleukin (IL)-15 stimulation. These data suggest that Shp-2 is relevant to IL-15 signaling also in T cells and, possibly, in other cytokines’ responses. Here, we thus propose to: 1) explore function and relevance of SHP-2 in cytokine signaling more broadly and 2) define the molecular events underlying the SHP-2-mediated activation of signaling cascades. This will significantly broaden our understanding of SHP-2’s mode of action and relevance in pathways important for immunity and immune disorders. Suggesting redundancy with other phosphatases, we recently found Shp-2 to be dispensable in vivo for signaling downstream of PD-1 (Programmed cell death 1), a clinically relevant IR. We thus propose to dissect PD-1 signaling through innovative approaches: 1) complex genetic models will allow to address, with unprecedented accuracy, the role of Shp-2 and other phosphatases in exhausted T cells in vivo and 2) highly sensitive affinity purification and mass spectrometry-based methods will be used to study the interactome of PD-1 in primary exhausted T cells genetically optimized to identify relevant binding partners; novel candidates will be evaluated as described in 1). We believe that these complementary approaches will enable us to identify functionally relevant interactors of PD-1, an essential step towards a molecular understanding and therapeutic targeting of this pathway crucial in the immuno-oncology field.