Extracellular FABP4 uptake by endothelial cells is dependent on cytokeratin 1 expression.

AIMS: The aim of this study is to determine the physical and functional interplay between fatty acid-binding protein 4 (FABP4) and its membrane receptor-like candidate protein, cytokeratin 1 (CK1), and to determine the effect of hindering CK1-mediated FABP4 cellular uptake on non-disturbed or metabolically stressed endothelial cells. METHODS: We monitored the direct interaction between FABP4 and CK1 using surface plasmon resonance, and the effects of blocking exogenous FABP4 (eFABP4) cellular uptake were determined by using specific siRNA to knock down the expression of CK1 in human umbilical vein endothelial cells (HUVECs). The expression and nuclear translocation of transcription factors involved in oxidative stress (NRF2) and inflammation (p65 subunit of NF-ĸB transcription factor) were determined by Western blotting analysis. RESULTS: Our data showed that FABP4 and CK1 bind to each other and that the putative FABP4 binding domain would be within the 151GIQEVTINQSLLQPLNVEID170 CK1 sequence. We determined that in non-disturbed or metabolically stressed endothelial cells, eFABP4 regulates the cellular response to oxidative stress. In addition, we also found that in the presence of palmitate, eFABP4 increases the pro-inflammatory effects induced by palmitate per se, probably due to an increase in the transport of palmitate inside cells, suggesting that these FABP4-mediated pro-oxidative and pro-inflammatory effects are dependent on CK1 expression. CONCLUSIONS: We demonstrated that CK1 facilitates eFABP4 cellular uptake in endothelial cells. Therefore, the CK1-targeted inhibition of exogenous FABP4 cellular uptake might be a potential therapeutic strategy to protect endothelial cells against FABP4-induced activation of inflammation and oxidative stress.

The peritumoural adipose tissue microenvironment and cancer. The roles of fatty acid binding protein 4 and fatty acid binding protein 5.

The adipose tissue microenvironment plays a key role in tumour initiation and progression because it provides fatty acids and adipokines to tumour cells. The fatty acid-binding protein (FABP) family is a group of small proteins that act as intracellular fatty acid transporters. Adipose-derived FABPs include FABP4 and FABP5. Both have an important role in lipid-related metabolic processes and overexpressed in many cancers, such as breast, prostate, colorectal and ovarian. Moreover, their expression in peritumoural adipose tissue is deregulated, and their circulating levels are upregulated in some tumours. In this review, we discuss the role of the peritumoural adipose tissue and the related adipokines FABP4 and FABP5 in cancer initiation and progression and the possible pathways implicated in these processes.