Required to control the activity of various transcription factors through their sequestration in the cytoplasm. Retains nuclear Zic proteins ZIC1, ZIC2 and ZIC3 in the cytoplasm and inhibits their transcriptional activation (By similarity). Modulates the expression from cellular promoters. Binds to the axin complex, resulting in an increase in the level of free beta-catenin (PubMed:12192039). Affects axin regulation of the WNT and JNK signaling pathways (PubMed:12192039). Involved in the development of lymphatic vessel valves (By similarity). Required to promote lymphatic endothelial cell migration, in a process that involves down-regulation of integrin beta 1 activation and control of cell adhesion to the extracellular matrix (PubMed:35235341). Regulates the activity of mechanosensitive Piezo channel (PubMed:37590348). {ECO:0000250|UniProtKB:Q8BX65, ECO:0000269|PubMed:12192039, ECO:0000269|PubMed:35235341, ECO:0000269|PubMed:37590348}. (Microbial infection) Modulates the expression from viral promoters. Down-regulates Tat-dependent transcription of the human immunodeficiency virus type 1 (HIV-1) LTR by interacting with HIV-1 Tat and Rev and impairing their nuclear import, probably by rendering the NLS domains inaccessible to importin-beta (PubMed:12944466, PubMed:16260749, Ref.6). Also stimulates activation of human T-cell leukemia virus type I (HTLV-I) LTR (PubMed:10671520). {ECO:0000269|PubMed:10671520, ECO:0000269|PubMed:12944466, ECO:0000269|PubMed:16260749, ECO:0000269|Ref.6}. This is the function of Ensembl gene identifier ENSG00000135272 (MDFIC, MyoD family inhibitor domain containing).