HLA complex group 22 (HCG22)

HLA complex group 22 (HCG22) refers to a genetic locus on human chromosome 6 near the HLA region. There is substantial ambiguity about its molecular nature. Some sources describe HCG22 as a non-protein-coding gene[5][3], while functional studies have characterized an mRNA and predicted protein product that is a small, secreted, O-glycosylated, mucin-like glycoprotein (provisionally called PBMUCL2), related to the peritrophin-A mucin family[1]. The protein backbone is predicted to be 26 kDa but appears as a 70–75 kDa mucin-type glycoprotein on Western blot due to glycosylation[1]. It is not a known receptor, enzyme, transporter, or typical therapeutic target. Expression of HCG22 can be stimulated by IL-1β and inhibited by TGF-β and glucocorticoids in human trabecular meshwork cells[1]. Genetic variants upstream or within the signal peptide of HCG22 have been associated with glucocorticoid-induced ocular hypertension, suggesting a role in steroid responsiveness and risk for glaucoma[1]. The gene lies close to known mucin gene clusters (MUC21, MUC22), but the functional annotation in reference databases remains inconsistent: some label it a non-coding RNA, others annotate a protein-coding transcript. No drugs are known to target HCG22. There are no unique safety concerns, but the significance of genetic polymorphisms may serve as a biomarker for steroid response in ocular hypertension[1]. Note on ambiguity: There is conflicting information about whether HCG22 encodes a small, secreted mucin-like protein or is a non-coding RNA locus[1][5][3]. Most reference databases now classify HCG22 as a non-protein-coding gene, but experimental evidence indicates protein-coding potential with functional relevance to ocular disease[1]. This inconsistent annotation is a significant concern for biomedical applications (is_incorrect: true). Summary: HCG22 is not a classical drug target and should not be classified as a receptor or enzyme. It is of research interest primarily for its association with glucocorticoid-induced ocular hypertension and possible risk for glaucoma, mediated by a mucin-like protein product whose existence remains debated in the literature and gene databases[1][5][3].

Other names

Protein PBMUCL2G2PBMUCL2FLJ37114HCG22HLA complex group 22Panbronchiolitis-related mucin-like protein 2panbronchiolitis related mucin-like 2HLA complex group 22 (non-protein coding)protein PBMUCL2