The function of JMJD1C (jumonji domain containing 1C, Ensembl gene identifier ENSG00000171988) is as follows. Demethylates lysine in proteins, such as STAT3 or MDC1 (By similarity) (PubMed:24240613). Demethylates MDC1, thereby promoting MDC1-RNF8 interaction and facilitating RNF8-dependent MDC1 ubiquitination essential for double-strand break (DSB) repair (PubMed:24240613). Demethylation of STAT3 at 'Lys-140' facilitates its interactions with the phosphatase PTPN6 and restrains STAT3 activation (By similarity). It is uncertain whether JMJD1C removes methyl groups from histone proteins as the other JMJD1/KDM3 proteins do (PubMed:23593242, PubMed:24240613, PubMed:32034158). Nevertheless, JMJD1C may act as a context-specific histone demethylase. Implicated in lipogenic gene transcription in the liver, where USF1 recruits JMJD1C to lipogenic promoters in response to insulin or feeding stimuli, thereby potentially promoting H3K9me2 demethylation and enhancing chromatin accessibility (PubMed:32034158). Post-translational modifications may regulate JMJD1C's enzymatic activity, contributing to its context-specific functions (PubMed:32034158). Alternatively, JMJD1C may influence chromatin regulation indirectly, acting as a scaffold or co-regulator that recruits or stabilizes other active demethylase complexes modifying histone marks (PubMed:24240613). Plays an indispensable role in spermatogenesis (By similarity). {ECO:0000250|UniProtKB:Q69ZK6, ECO:0000269|PubMed:23593242, ECO:0000269|PubMed:24240613, ECO:0000269|PubMed:32034158}. [Isoform 3]: Coactivator of androgen receptor. .