XIAP-associated factor 1 interacts with and attenuates the trans-activity of four and a Half LIM protein 2

The roles of FHL2 in cancer

LIM domain protein 2, also known as LIM protein FHL2, is a member of the LIM-only family. Due to its LIM domain protein characteristics, FHL2 is capable of interacting with various proteins and plays a crucial role in regulating gene expression, cell growth, and signal transduction in muscle and cardiac tissue. In recent years, mounting evidence has indicated that the FHLs protein family is closely associated with the development and occurrence of human tumors. On the one hand, FHL2 acts as a tumor suppressor by down-regulating in tumor tissue and effectively inhibiting tumor development by limiting cell proliferation. On the other hand, FHL2 serves as an oncoprotein by up-regulating in tumor tissue and binding to multiple transcription factors to suppress cell apoptosis, stimulate cell proliferation and migration, and promote tumor progression. Therefore, FHL2 is considered a double-edged sword in tumors with independent and complex functions. This article reviews the role of FHL2 in tumor occurrence and development, discusses FHL2 interaction with other proteins and transcription factors, and its involvement in multiple cell signaling pathways. Finally, the clinical significance of FHL2 as a potential target in tumor therapy is examined.

Role of FHL2 in digestive system malignancies

FHL2 is a scaffold protein that regulates signal transduction and gene transcription, and it has typical structural features of FHL proteins. Each FHL protein contains four half-LIM domains, and different LIM domains can bind to different proteins, which can activate or inhibit the activities of transcription factors such as P53 and serum response factors, and then influences the development of tumors. Previous studies have found that FHL2 has a complex biological role in tumorigenesis, and may promote or suppress tumor development in different types of tumors. In this article, we review the role of FHL2 in digestive system malignancies.

KLF8 promotes tumorigenesis, invasion and metastasis of colorectal cancer cells by transcriptional activation of FHL2

The transcription factor Krüppel-like factor (KLF)8 plays an important role in the formation of several human tumors, including colorectal cancer. We recently identified four-and-a-half LIM protein 2 (FHL2) as a critical inducer of the epithelial-to-mesenchymal transition (EMT) and invasion. However, the molecular mechanism by which KLF8 affects FHL2-mediated tumor proliferation, EMT and metastasis remains unknown. Here, we showed that KLF8 overexpression promoted EMT and metastatic phenotypes. KLF8 expression was stimulated by transforming growth factor (TGF)-β1. Moreover, KLF8 acted as a potential EMT inducer by stimulating vimentin expression and inducing a loss of E-cadherin in stable KLF8-transfected cells. KLF8 overexpression induced a strong increase in FHL2 expression, and a positive correlation between the expression patterns of KLF8 and FHL2 was observed in CRC cells. Promoter reporter and chromatin immunoprecipitation (ChIP) assays demonstrated that KLF8 directly bound to and activated the human FHL2 gene promoter. However, siRNA-mediated repression of FHL2 in KLF8-overexpressing cells reversed the EMT and the proliferative and metastatic phenotypes. In vivo, KLF8 promoted FHL2-mediated proliferation and metastasis via orthotopic implantation. Taken together, this work identified KLF8-induced FHL2 activation as a novel and critical signaling mechanism underlying human breast/colorectal cancer invasion and metastasis.

The XAF1 tumor suppressor induces autophagic cell death via upregulation of Beclin-1 and inhibition of Akt pathway

Autophagy is designated as type II programmed cell death and may confer a tumor-suppressive function. Our previous studies have shown that XIAP-associated factor 1 (XAF1) induced apoptosis and inhibited tumor growth in gastric cancer cells. In this study, we investigated the effect of XAF1 on the induction of autophagy in gastric cancer cells. We found that adenovirus vector-mediated XAF1 (adeno-XAF1) expression markedly induced autophagy, upregulated the level of Beclin-1 and inhibited phospho-Akt and phospho-p70S6K in gastric cancer cells. The downregulation of Beclin 1 or 3-methyladenine treatment suppressed adeno-XAF1-induced autophagy, but significantly enhanced adeno-XAF1-induced apoptosis. A pan-caspase inhibitor prevented adeno-XAF1-induced apoptosis, but significantly increased adeno-XAF1-induced autophagy. Furthermore, adeno-XAF1 induced autophagy in xenograft tumor and inhibited tumor growth. Our results document that adeno-XAF1 induces autophagy through upregulation of Beclin 1 expression and inhibition of Akt/p70S6K pathway, and reveal a new mechanism of XAF1 tumor suppression.