Probable GTP-binding protein (PubMed:24286120). Functions in innate immunity and more specifically the inflammatory response as a regulator of the Toll-like receptor TLR2 and TLR4 signaling pathways (PubMed:26599367, PubMed:28471450, PubMed:28609714). Negatively regulates the part of the TLR4 signaling pathway that leads to the activation of the transcription factor AP-1. By retaining the phosphatase complex PP2A into the cytoplasm, prevents the dephosphorylation of the AP-1 subunit JUN which is required for proper activation of the transcription factor (PubMed:28609714). Both inhibits and activates the TLR2-dependent signaling pathway (PubMed:26599367). Positively regulates the TLR2 signaling pathway to activate specifically the downstream p38 and JNK MAP kinases and promote the polarization of macrophages toward the pro-inflammatory M1 phenotype (PubMed:28471450). It may also play a role in the regulation of inflammation induced by high glucose through the PKB/AKT signaling pathway (PubMed:29168081). Also involved in erythrocyte differentiation through activation of the ERK1/ERK2 signaling pathway (PubMed:23327923). Interacts with RAF1 (PubMed:23327923). Interacts with HSPD1 (PubMed:24286120). Interacts with PPP2CA; retains PPP2CA into the cytoplasm and excludes it from the nucleus (PubMed:28609714). Interacts with PPP2R2A; the interaction is direct (PubMed:28609714). Interacts with PJA2 (PubMed:28471450). Ubiquitously expressed. Overexpressed in malignant fibrous histiocytomas (PubMed:9973190). Expressed in red blood cells (at protein level) (PubMed:23327923). Up-regulated during erythroid cells differentiation (at protein level) (PubMed:23327923). Up-regulated upon Toll-like receptor TLR2 stimulation (PubMed:26599367). Up-regulated in macrophages upon M. tuberculosis infection (PubMed:20616063). Up-regulated upon sepsis (PubMed:26599367). Up-regulated by glucose (PubMed:29168081). Ubiquitinated. Ubiquitination by PJA2 does not lead MFHAS1 to proteasomal degradation but positively regulates its function in polarization of macrophages. A chromosomal aberration involving MFHAS1 may be a cause of B-cell lymphoma. Translocation t(8;14)(p23.1;q21) with a cryptic exon named '14q21 element'. The resulting fusion protein named 'chimeric MASL1' is tumorigenic in nude mice.