The function of FBXO4 (F-box protein 4, ENSG00000151876) is as follows. Substrate recognition component of a SCF (SKP1-CUL1-F-box protein) E3 ubiquitin-protein ligase complex that mediates the ubiquitination and subsequent proteasomal degradation of target proteins (PubMed:10531035, PubMed:18598945, PubMed:20181953, PubMed:29142209). Promotes ubiquitination of cyclin-D1 (CCND1) and its subsequent proteasomal degradation (PubMed:18598945). However, it does not act as a major regulator of CCND1 stability during the G1/S transition (By similarity). Recognizes TERF1 and promotes its ubiquitination together with UBE2D1 (PubMed:16275645, PubMed:20159592). Promotes ubiquitination of FXR1 following phosphorylation of FXR1 by GSK3B, leading to FXR1 degradation by the proteasome (PubMed:29142209). {ECO:0000250|UniProtKB:Q8CHQ0, ECO:0000269|PubMed:10531035, ECO:0000269|PubMed:16275645, ECO:0000269|PubMed:18598945, ECO:0000269|PubMed:20159592, ECO:0000269|PubMed:20181953, ECO:0000269|PubMed:29142209}.