Substrate recognition component of a SCF (SKP1-CUL1-F-box protein) E3 ubiquitin-protein ligase complex which mediates the ubiquitination and subsequent proteasomal degradation of PDCD1/PD-1, thereby regulating T-cells-mediated immunity (PubMed:30487606). Required for anti-tumor activity of T-cells by promoting the degradation of PDCD1/PD-1; the PDCD1-mediated inhibitory pathway being exploited by tumors to attenuate anti-tumor immunity and facilitate tumor survival (PubMed:30487606). May indirectly stimulate the activity of transcription factor KLF7, a regulator of neuronal differentiation, without promoting KLF7 ubiquitination (PubMed:14729953, PubMed:16990251). Protein modification; protein ubiquitination. Part of the SCF (SKP1-CUL1-F-box) E3 ubiquitin-protein ligase complex SCF(FBXO38) composed of CUL1, SKP1, RBX1 and FBXO38 (By similarity). Interacts with KLF7 (PubMed:14729953). Interacts with PDCD1/PD-1 (By similarity). Accumulates predominantly in the cytosol (PubMed:16990251). Exported from the nucleus in a XPO1/CRM1-dependent manner (PubMed:16990251). Expressed at high levels in embryo (developing brain, spinal chord, branchial arms and limbs) (PubMed:14729953). Widely expressed at low levels in adult tissues, with highest expression in testis. Expressed in postmeiotic spermatids (PubMed:14729953). In embryo expressed at 11 dpc, 15 dpc and 17 dpc. Up-regulated by IL2 (PubMed:30487606). Down-regulated in tumor-infiltrating T-cells (PubMed:30487606). Conditional deletion in T-cells does not affect the development, peripheral homeostasis and population of memory T-cells, but leads to faster tumor progression (PubMed:30487606). Faster tumor progression is caused by higher levels of Pdcd1/PD-1 in tumor-infiltrating T-cells (PubMed:30487606).