Unravelling the Intricate Roles of FAM111A and FAM111B: From Protease-Mediated Cellular Processes to Disease Implications.

Proteases are critical enzymes in cellular processes which regulate intricate events like cellular proliferation, differentiation and apoptosis. This review highlights the multifaceted roles of the serine proteases FAM111A and FAM111B, exploring their impact on cellular functions and diseases. FAM111A is implicated in DNA replication and replication fork protection, thereby maintaining genome integrity. Additionally, FAM111A functions as an antiviral factor against DNA and RNA viruses. Apart from being involved in DNA repair, FAM111B, a paralog of FAM111A, participates in cell cycle regulation and apoptosis. It influences the apoptotic pathway by upregulating anti-apoptotic proteins and modulating cell cycle-related proteins. Furthermore, FAM111B's association with nucleoporins suggests its involvement in nucleo-cytoplasmic trafficking and plays a role in maintaining normal telomere length. FAM111A and FAM111B also exhibit some interconnectedness and functional similarity despite their distinct roles in cellular processes and associated diseases resulting from their dysfunction. FAM111A and FAM111B dysregulation are linked to genetic disorders: Kenny-Caffey Syndrome type 2 and Gracile Bone Dysplasia for FAM111A and POIKTMP, respectively, and cancers. Therefore, the dysregulation of these proteases in diseases emphasizes their potential as diagnostic markers and therapeutic targets. Future research is essential to unravel the intricate mechanisms governing FAM111A and FAM111B and explore their therapeutic implications comprehensively.

FAM111B dysregulation promotes malignancy in fibrosarcoma and POIKTMP and a low-cost method for its mutation screening.

INTRODUCTION: Mutations in the uncharacterised human FAM111B gene are associated with POIKTMP, a rare multi-organ fibrosing disease. Recent studies also reported the overexpression of FAM111B in specific cancers. Moreover, FAM111B mutation screening may prove expensive in under-resourced facilities. Therefore, this study investigated its cellular function and dysfunction and described an inexpensive mutation screening method. MATERIALS AND METHODS: FAM111B expression was assessed in silico and validated in vitro in cell lines and primary skin fibroblasts from a South African POIKTMP-patient with the heterozygous FAM111B gene mutation: NM_198947.4: c.1861T>G (p. Tyr621Asp or Y621D) by qPCR and western blot. The cellular function of FAM111B was studied in HT1080 using various cell-based functional assays, and the Y621D mutation was genotyped by PCR-RFLP. RESULTS: Expression studies showed upregulated FAM111B mRNA and protein in the cancer cells. High FAM111B expression with robust nuclear localization occurred in HT1080. Additionally, expression data and cell-based assays indicated that FAM111B led to the upregulation of cell migration, decreased cell apoptosis, and modulatory effects on cell proliferation. Y621D mutation showed similar effects on cell migration but minimal impact on cell apoptosis. FAM111B mRNA and protein expression were markedly downregulated (p ≤ 0.05) in the POIKTMP-patient's fibroblasts. The PCR-RFLP method successfully genotyped Y621D gene mutation. DISCUSSION: FAM111B is a cancer-associated nuclear protein: Its modulation by mutations or overexpression may contribute to the malignancy of cancers and POIKTMP/fibrosis and poor clinical outcomes and represents a viable prognostic marker or therapeutic target. Furthermore, the PCR-RFLP method could prove a valuable tool for FAM111B mutation validation or screening in resource-constrained laboratories.

Proposed Cellular Function of the Human FAM111B Protein and Dysregulation in Fibrosis and Cancer.

FAM111B gene mutations are associated with a hereditary fibrosing poikiloderma known to cause poikiloderma, tendon contracture, myopathy, and pulmonary fibrosis (POIKTMP). In addition, the overexpression of FAM111B has been associated with cancer progression and poor prognosis. This review inferred the molecular function of this gene's protein product and mutational dysfunction in fibrosis and cancer based on recent findings from studies on this gene. In conclusion, FAM111B represents an uncharacterized protease involved in DNA repair, cell cycle regulation, and apoptosis. The dysregulation of this protein ultimately leads to fibrotic diseases like POIKTMP and cancers via the disruption of these cellular processes by the mutation of the FAM111B gene. Hence, it should be studied in the context of these diseases as a possible therapeutic target.

Mutations within the putative protease domain of the human FAM111B gene may predict disease severity and poor prognosis: A review of POIKTMP cases.

Mutations in the human FAM111B gene are associated with a rare, hereditary multi-systemic fibrosing disease, POIKTMP. To date, there are ten POIKTMP-associated FAM111B gene mutations reported in thirty-six patients from five families globally. To investigate the clinical significance of these mutations, we summarized individual cases by clinical features and position of the reported FAM111B gene mutations as those within and outside the putative protease domain (MWPPD and MOPPD respectively). MWPPD cases had more clinical manifestations than MOPPD (25 versus 18). Although the most common clinical features of poikiloderma, alopecia and hypohidrosis overall occurred in 94%, 86% and 75% of all cases with no significant differences between the MOPPD and MWPPD group, less common features included life-threatening (pulmonary fibrosis 47% vs. 13%; liver abnormalities specifically cirrhosis 26% vs. 7%) and physically disabling conditions (myopathy 53% vs. 20%; tendon contracture 55% vs. 7%) were more common in MWPPD cases. Similarly, the only 2 cases of POIKTMP with fatal pancreatic cancers were both only in the MWPPD group. This review thus suggests that mutations within the putative protease domain of the FAM111B protein are associated with a broader range of clinical features and may predict increased POIKTMP severity and a poorer prognosis.