The function of TMEM203 (transmembrane protein 203, ENSG00000187713) is as follows. Involved in the regulation of cellular calcium homeotasis (PubMed:25996873). Required for spermatogenesis (PubMed:25996873). Acts as a regulator of STING-mediated inflammatory signaling in macrophages (PubMed:31346090). Forms a complex with STING, promoting the activity of TBK1 kinase and the transcription factor IRF3, leading to activation of type I interferon expression (By similarity). {ECO:0000250|UniProtKB:Q8R235, ECO:0000269|PubMed:25996873, ECO:0000269|PubMed:31346090}.