Lipid droplets' functional protein caveolin-2 is associated with lipid metabolism-related molecule FABP5 and EMT marker E-cadherin in oral epithelial dysplasia

AIMS

To explore the accumulation of lipid droplets (LDs) and its relationship with lipid metabolism, and epithelial-mesenchymal transition (EMT) in the carcinogenesis processes in the oral cavity.

METHODS

LDs were stained by oil red O. Forty-eight oral squamous cell carcinomas (OSCC), 78 oral potentially malignant disorders (OPMDs) and 25 normal tissue sections were included to explore the LDs surface protein caveolin-2 and perilipin-3, lipid metabolism-related molecule FABP5 and EMT biomarker E-cadherin expression by immunohistochemical staining.

RESULTS

The accumulation of LDs was observed in OPMDs and OSCCs compared with normal tissues (p<0.05). In general, an increasing trend of caveolin-2, perilipin-3 and FABP5 expression was detected from the normal to OPMDs to OSCC groups (p<0.05). Additionally, caveolin-2, perilipin-3 and FABP5 expression were positively correlated with epithelial dysplasia in OPMDs, whereas E-cadherin positivity was negatively correlated with histopathological grade in both OPMDs and OSCC, respectively. A negative correlation of caveolin-2 (p<0.01, r =-0.1739), and FABP5 (p<0.01, r =-0.1880) with E-cadherin expression was detected. The caveolin-2 (p<0.0001, r=0.2641) and perilipin-3 (p<0.05, r=0.1408) staining was positively correlated with FABP5. Increased caveolin-2 expression was related to local recurrence and worse disease-free survival (p<0.05).

CONCLUSION

In the oral epithelial carcinogenesis process, LDs begin to accumulate early in the precancerous stage. LDs may be the regulator of FABP5-associated lipid metabolism and may closely related to the process of EMT; caveolin-2 could be the main functional protein.

Disorder in milk proteins: adipophilin and TIP47, important constituents of the milk fat globule membrane

Milk fat globules (MFGs), which are secreted by the epithelial cells of the lactating mammary glands, account for the most of the nutritional value of milk. They are enveloped by the milk fat globule membrane (MFGM), a complex structure consisting of three phospholipid membrane monolayers and containing various lipids. Depending on the origin of milk, specific proteins accounts for 5-70% of the MFGM mass. Proteome of MFGMs includes hundreds of proteins, with nine major components being adipophilin, butyrophilin, cluster of differentiation 36, fatty acid binding protein, lactadherin, mucin 1, mucin 15, tail-interacting protein 47 (TIP47), and xanthine oxidoreductase. Two of the MFGM components, adipophilin and TIP47, belong to the five-member perilipin family of lipid droplet proteins. Adipophilin is involved in the formation of cytoplasmic lipid droplets and secretion of MFGs. This protein is also related to the formation of other lipid droplets that exist in most cell types, playing an important role in the transport of lipids from ER to the surface of lipid droplets. TIP47 acts as a cytoplasmic sorting factor for mannose 6-phosphate receptors and is recruited to the MFGM. Therefore, both adipophilin and TIP47 are moonlighting proteins, each possessing several unrelated functions. This review focuses on the main functions and specific structural features of adipophilin and TIP47, analyzes similarities and differences of these proteins among different species, and describes these proteins in the context of other members of the perilipin family.Communicated by Ramaswamy H. Sarma.