Diabetic kidney disease (DKD) is appeared to be higher risk of declining kidney function compared to non-diabetic kidney disease with same magnitude of albuminuria. Epithelial-mesenchymal transition (EMT) program of tubular epithelial cells (TECs) could be important for the production of the extracellular matrix in the kidney. Caveolin-1 (CAV1), dipeptidyl peptidase-4 (DPP-4) and integrin β1 have shown to be involved in EMT program. Here, we found diabetic kidney is prone for albuminuria-induced TECs damage and DPP-4 plays a vital role in such parenchymal damages in diabetic mice. The bovine serum albumin (BSA) injection induced severe TECs damage and altered expression levels of DPP-4, integrin β1, CAV1, and EMT programs including relevant microRNAs in type 1 diabetic CD-1 mice when compared to non-diabetic mice; teneligliptin (TENE) ameliorated these alterations. TENE suppressed the close proximity among DPP-4, integrin β1 and CAV1 in a culture of HK-2 cells. These findings suggest that DPP-4 inhibition can be relevant for combating proteinuric DKD by targeting the EMT program induced by the crosstalk among DPP-4, integrin β1 and CAV1.

Dipeptidyl peptidase (DPP)-4 is a multifunctional glycoprotein involved in various biological and pathologic processes. DPP-4 has been widely recognized as a therapeutic target for type 2 diabetes mellitus but is also implicated in the development of human malignancies. Here, we show that inhibition of DPP-4 accelerates breast cancer metastasis via induction of CXCL12/CXCR4, which activates mTOR to promote epithelial-mesenchymal transition (EMT). In cultured cells, DPP-4 knockdown induced EMT and cell migration. Treatment with the DPP-4 inhibitor KR62436 (KR) promoted primary tumor growth and lung metastasis in a 4T1 tumor allograft mouse model; DPP-4 knockdown in 4T1 cells displayed similar phenotypes in vivo and in vitro. KR treatment enhanced the levels of CXCL12/CXCR4 and phosphorylated mTOR, which were associated with the induction of EMT in metastatic cancer cells. KR-induced EMT in cancer cells was inhibited by treatment with the CXCR4 inhibitor AMD3100 or the mTOR inhibitor rapamycin, and AMD3100 suppressed KR-induced metastasis in vivo. Our findings suggest that DPP-4 plays a significant role in cancer biology and that inhibition of DPP-4 promotes cancer metastasis via induction of the CXCL12/CXCR4/mTOR/EMT axis. SIGNIFICANCE: These findings reveal that inhibition of DPP-4 increases the metastatic potential of breast cancer. This is especially important given the potential use of DPP-4 inhibition as a therapeutic strategy for type 2 diabetes.

Dipeptidyl peptidase (DPP)-4, a molecular target of DPP-4 inhibitors, which are type 2 diabetes drugs, is expressed in a variety of cell types, tissues and organs. DPP-4 has been shown to be involved in cancer biology, and we have recently shown that a DPP-4 inhibitor promoted the epithelial mesenchymal transition (EMT) in breast cancer cells. The EMT is known to associate with chemotherapy resistance via the induction of ATP-binding cassette (ABC) transporters in cancer cells. Here, we demonstrated that deficiency in DPP-4 promoted chemotherapy resistance via the CXCL12/CXCR4/mTOR axis, activating the TGFβ signaling pathway via the expression of ABC transporters. DPP-4 inhibition enhanced ABC transporters in vivo and in vitro. Doxorubicin (DOX) further induced ABC transporters in DPP-4-deficient 4T1 cells, and the induction of ABC transporters was suppressed by either the CXCR4 inhibitor AMD3100, the mTOR inhibitor rapamycin or a neutralizing TGFβ (1, 2 and 3) antibody(N-TGFβ). Knockdown of snail, an EMT-inducible transcription factor, suppressed ABC transporter levels in DOX-treated DPP-4-deficient 4T1 cells. In an allograft mouse model, however, the effects of DOX in either primary tumor or metastasis were not statistically different between control and DPP-4-kd 4T1. Taken together, our findings suggest that DPP-4 inhibitors potentiate chemotherapy resistance via the induction of ABC transporters by the CXCL12/CXCR4/mTOR/TGFβ signaling pathway in breast cancer cells.

Autophagy plays a complex role in breast cancer cell survival, metastasis, and chemotherapeutic resistance. Dipeptidyl peptidase (DPP)-4, a therapeutic target for type 2 diabetes mellitus, is also involved in autophagic flux. The potential influence of DPP-4 suppression on cancer biology remains unknown. Here, we report that DPP-4 deficiency promotes breast cancer cell survival via the induction of autophagy by the C-X-C motif chemokine 12 (CXCL12)/C-X-C receptor 4 (CXCR4)/mammalian target of rapamycin (mTOR)/hypoxia inducible factor (HIF)-1α axis. DPP-4 knockdown and DPP-4 inhibitor KR62436 (KR) treatment both increased the levels of LC3II and HIF-1α in cultured human breast and mouse mammary cancer cells. The KR-induced autophagic phenotype in cancer cells was inhibited by treatment with the CXCR4 inhibitor AMD3100 and rapamycin. HIF-1α knockdown also suppressed breast cancer autophagy induced by KR. The autophagy inhibitor 3-methyladenine significantly blocked the KR-mediated suppression of cleaved caspase-3 levels and apoptosis in breast cancer cell lines. Finally, we found that the metformin-induced apoptosis of DPP-4-deficient 4T1 mammary cancer cells was associated with the suppression of autophagy. Our findings identify a novel role for DPP-4 inhibition in the promotion of breast cancer survival by inducing CXCL12/CXCR4/mTOR/HIF-1α axis-dependent autophagy. Metformin is a potential drug that counteracts the breast cancer cell survival system.

Integrin β1 and dipeptidyl peptidase (DPP)-4 play roles in endothelial cell biology. Vascular endothelial growth factor (VEGF)-A inhibits endothelial-to-mesenchymal transition (EndMT) through VEGF-R2, but through VEGF-R1 promotes EndMT by reducing the bioavailability of VEGF-A. Here we tested whether DPP-4-integrin β1 interactions have a role in EndMT in the renal fibrosis of diabetic nephropathy. In streptozotocin-induced fibrotic kidneys in diabetic CD-1 mice, levels of endothelial DPP-4, integrin β1, and phospho-integrin β1 were all higher and associated with plasma cystatin C elevation. The DPP-4 inhibitor linagliptin ameliorated kidney fibrosis, reduced plasma cystatin C levels, and suppressed endothelial levels of DPP-4, integrin β1, and phospho-integrin β1. In cultured endothelial cells, DPP-4 and integrin β1 physically interacted. Suppression of DPP-4 by siRNA was associated with suppression of integrin β1 and vice versa. Knockdown of either integrin β1 or DPP-4 resulted in the silencing of TGF-β2-induced TGF-β receptor heterodimer formation, smad3 phosphorylation, and EndMT. DPP-4 negatively regulated endothelial viability signaling by VEGF-R2 suppression and VEGF-R1 induction in endothelial cells. Thus, DPP-4 and integrin β1 interactions regulate key endothelial cell signal transduction in both physiological and pathological conditions including EndMT. Hence, inhibiting DPP-4 may be a therapeutic target for treating kidney fibrosis in diabetes.

Dipeptidyl peptidase (DPP)-4 plays an important role in endothelial cell biology. We have shown that the DPP-4 inhibitor Linagliptin can inhibit the endothelial-mesenchymal transition (EndMT) and ameliorate diabetic kidney fibrosis associated with the suppression of DPP-4 protein levels via the induction of miR-29. The current study demonstrated that such effects of Linagliptin on endothelial cell profibrotic programs were drug-specific but not class effects. In the cell-free system, both Linagliptin and Sitagliptin inhibited recombinant DPP-4 activity in a concentration-dependent manner. Linagliptin can inhibit all of the following: DPP-4 activity and protein level, integrin β1 protein levels, EndMT, and DPP-4 3'UTR activity; Sitagliptin, however, inhibited none of these in the current study. Additionally, TGF-β2 induced both the induction of VEGF-R1 and the suppression of VEGF-R2 levels in endothelial cells, and both were inhibited by Linagliptin but not by Sitagliptin. miR-29, the miR that negatively regulates the 3'UTR of DPP-4 mRNA, was suppressed by TGF-β2 and restored by Linagliptin but not by Sitagliptin. Following the overexpression of pCMV-DPP-4-GFP and pCMV6-Myc-DPP-4 in endothelial cells, the proximity of Myc-DPP-4 and DPP-4-GFP was suppressed by Linagliptin but not by Sitagliptin, suggesting that only Linagliptin inhibited the homo-dimer formation of DPP-4 in endothelial cells; this difference in activity between the two gliptins could explain their diverse effects on endothelial cell biology. In conclusion, each of the DPP-4 inhibitors may have unique drug-specific effects.

Linagliptin is a selective dipeptidyl peptidase (DPP)-4 inhibitor capable of successfully regulating blood glucose levels. The cardiovascular protective effects of several DPP-4 inhibitors have been shown in preclinical studies; however, the detailed influence of DPP-4 inhibitors on diabetic pathological alterations in cardiac tissue has not yet been elucidated.

N-acetyl-seryl-aspartyl-lysyl-proline (AcSDKP) is an endogenous antifibrotic peptide. We found that suppression of AcSDKP and induction of dipeptidyl peptidase-4 (DPP-4), which is associated with insufficient levels of antifibrotic microRNA (miR)s in kidneys, were imperative to understand the mechanisms of fibrosis in the diabetic kidneys. Analyzing streptozotocin (STZ)-induced diabetic mouse strains, diabetic CD-1 mice with fibrotic kidneys could be differentiated from less-fibrotic diabetic 129Sv mice by suppressing AcSDKP and antifibrotic miRs (miR-29s and miR-let-7s), as well as by the prominent induction of DPP-4 protein expression/activity and endothelial to mesenchymal transition. In diabetic CD-1 mice, these alterations were all reversed by AcSDKP treatment. Transfection studies in culture endothelial cells demonstrated crosstalk regulation of miR-29s and miR-let-7s against mesenchymal activation program; such bidirectional regulation could play an essential role in maintaining the antifibrotic program of AcSDKP. Finally, we observed that AcSDKP suppression in fibrotic mice was associated with induction of both interferon-γ and transforming growth factor-β signaling, crucial molecular pathways that disrupt antifibrotic miRs crosstalk. The present study provides insight into the physiologically relevant antifibrotic actions of AcSDKP via antifibrotic miRs; restoring such antifibrotic programs could demonstrate potential utility in combating kidney fibrosis in diabetes.