TGF-β downregulates antigen processing and presentation genes and MHC I surface expression through a Smad3-dependent mechanism

Abstract

Regulation of MHC I surface expression by TGF-β is important for controlling cell-mediated immune responses, but how TGF-β downregulates MHC I is unknown. We investigated this mechanism using flow cytometry and RNA-sequencing to identify the major TGF-β signaling pathway and target genes involved. All three isoforms of TGF-β were found to have similar abilities to downregulate constitutive MHC I surface expression. Inhibiting the type I TGF-β receptor, ALK5, as well the canonical TGF-β signaling molecule Smad3, prevented TGF-β from downregulating MHC I surface expression. RNA-sequencing from horse and human mesenchymal stem cells revealed that multiple genes associated with antigen processing and presentation were downregulated in TGF-β-treated cells with B2M and ERAP1 being downregulated in both species. While downregulation of MHC I surface expression a slow process that continued past 24 hours after TGF-β treatment, downregulation of gene expression of ERAP1 occurred within 12 hours after treatment. B2M expression was not consistently downregulated until after 24 hours and TAP2 expression was inconsistent over a 72-hour period, although it was significantly downregulated at 12 hours after TGF-β treatment. This data supports that TGF-β downregulates antigen processing and presentation genes resulting in decreased surface expression of MHC I through a Smad3-dependent mechanism.

Acis-regulatory element regulatesERAP2expression through autoimmune disease risk SNPs

“…In light of the fact that disease-associated SNPs affect ERAP2 expression independently of rs2248374, ERAP2 may be implicated in autoimmunity not because it is expressed in susceptible individuals but because it is expressed at higher levels (20,31). It corresponds with the notion that pro-inflammatory cytokines, such as interferons, upregulate ERAP2 significantly, while regulatory cytokines, like TGF-β, downregulate it, or that ERAP2 is increased in lesions of autoimmune patients (56)(57)(58).…”

A cis-regulatory element regulates ERAP2 expression through autoimmune disease risk SNPs

“… 20 , 37 It corresponds with the notion that pro-inflammatory cytokines, such as interferons, upregulate ERAP2 significantly, while regulatory cytokines, like transforming growth factor β, downregulate it, or that ERAP2 is increased in lesions of autoimmune patients. 54 , 55 Overexpression of ERAP2 may be exploited therapeutically by lowering its concentration in conjunction with local pharmacological inhibition of the enzymatic activity. 56…”

Unveiling the Immunogenicity of Ovarian Tumors as the Crucial Catalyst for Therapeutic Success

“…Importantly, TGF β1 targets the APM molecules in cancer cells by downregulating the H2 complex (MHC I in mouse), B2m, Tap1, and Tap2 shown in an in vitro model of CCK168 squamous cell cancer cells [127]. In human bone marrow-derived stem cells, two APM components, B2M and ERAP1, were downregulated following TGF β1 treatment [129]. Mouse PyMT tumor cells that were forced to undergo EMT through the upregulation of EMT-TFs ZEB1 or SNAIL in vitro also showed a marked decrease in B2M protein, a crucial co-factor for MHC I stability and antigen presentation on the cell surface [106].…”

“…Inhibition of Smad3 via a selective inhibitor of Smads (SIS3-HCI) in human bone marrow-derived stem cells resulted in the attenuation of TGF β1 s ability to downregulate MHC I expression, indicating the importance of SMAD2/3 signaling in mediating TGF β1's actions on suppressing APM [129]. Whether the downregulation of APM gene expression is dependent on EMT remains unclear, and it may well be that TGF β pathway activation promotes EMT and suppresses APM via independent mechanisms.…”