Effect of TGFβ-ITGB6 feedback loop on liver metastasis in SMAD4 wild-type pancreatic cancer

Pancreatic cancer (PC) is among the deadliest digestive malignancies, with over half of patients showing liver metastases at diagnosis. Understanding the molecular mechanisms underlying PC liver metastasis is crucial for improving patient prognosis and extending survival. This study aimed to elucidate the role of integrin subunit beta 6 (ITGB6), a downstream target of transforming growth factor-β (TGFβ) signaling, in PC progression and metastasis, particularly focusing on its involvement in liver metastasis.

First, ITGB6 was identified as a key TGFβ-pathway gene linked to liver metastasis in PC, with its enrichment further confirmed by SMAD family member 4 ( SMAD4 )-based subgroup analysis. A total of 37 paired clinical PC and adjacent normal tissue samples were obtained from patients who underwent surgical resection at Peking Union Medical College Hospital, and immunohistochemistry (IHC) was performed to evaluate ITGB6 expression and its correlation with clinicopathological features. In vitro assays, including cell proliferation, apoptosis detection, and cell migration and invasion assays, were conducted to evaluate the role of ITGB6 in PC cell behavior. A SMAD4 wild-type (WT) PC cell line stably overexpressing ITGB6 was established, and its in vivo role was assessed using subcutaneous and liver metastasis xenograft models. To explore the transcriptional regulation of ITGB6 by TGFβ, chromatin immunoprecipitation followed by quantitative polymerase chain reaction (ChIP-qPCR) and dual-luciferase reporter assays were performed. The effect of ITGB6-expressing PC cells on hepatic stellate cell (HSC) activation was evaluated using enzyme-linked immunosorbent assay (ELISA), Western blotting, and IHC. Finally, the therapeutic potential of targeting ITGB6 was preliminarily assessed using a monoclonal antibody intervention strategy.

TGFβ upregulates ITGB6 expression through a SMAD4-dependent pathway. Elevated ITGB6 expression not only promotes the migration and invasion of PC cells but also activates HSCs, thereby establishing a fibrotic microenvironment favorable for metastatic colonization. In mouse models, administration of an ITGB6 monoclonal antibody significantly attenuated HSC activation and suppressed the formation of liver metastases. Therefore, ITGB6 serves as a key downstream effector of TGFβ-mediated metastasis and represents a promising therapeutic target for liver metastasis in PC.

The TGFβ-ITGB6 positive feedback axis plays a critical role in liver metastasis of SMAD4 WT PC, highlighting ITGB6 as a potential therapeutic target, especially for patients with intact SMAD4 function.