Implication of BBM lipid composition and fluidity in mitigated alkaline phosphatase activity in renal cell carcinoma Ujjawal Sharma • Shrawan Kumar Singh • Deeksha Pal • Ragini Khajuria • Arup Kumar Mandal • Rajendra Prasad Received: 23 March 2012 / Accepted: 7 July 2012 / Published online: 19 July 2012 Ó Springer Science+Business Media, LLC. 2012 Abstract Previous study has documented reduced alka- line phosphatase (ALP) activity in brush border membrane (BBM) isolated from renal cell carcinoma (RCC). Dimin- ished activity of ALP is associated with alteration in both increased K m as well as decreased V max of enzyme suggests that there may be a change in the conformation of enzyme as well as decreased number of ALP active molecules. The present study was conducted to find out any role of BBM lipid composition and its fluidity in diminished activity of alkaline phosphatase in renal cell carcinoma. Total phos- pholipids and glycolipids were significantly augmented in BBM from RCC as compared to control. Fractional anal- ysis of total phospholipids revealed significantly increased phosphatidylethanolamine. Decreased fractions of sphin- gomyelin and phosphatidylinositol were observed. Cho- lesterol-to-total phospholipid molar ratios in tumor BBM was a significantly lower in tumor BBM. A significant reduction in polarization and microviscosity was found in BBM from RCC. Therefore, we conclude that alteration in membrane lipid composition and fluidity may play a substantial role in reduced activity of ALP in RCC. Keywords Alkaline phosphatase Á Renal cell carcinoma Á Brush border membrane Á Membrane fluidity Á Lipid composition Introduction Renal cell carcinoma (RCC) is the most common renal tumor accounting for approximately 3 % of adult malig- nancies and constitutes 90 % of all renal malignancies [1]. Electron microscopy studies documented that human renal cell carcinoma originated from epithelial cells of proximal convoluted tubules [2]. Alkaline phosphatases (orthopho- sphoric-monoester phosphohydrolase, alkaline optimum, EC 3.1.3.1), are cell surface glycoproteins that hydrolyze a variety of monophosphate esters [3]. Four major alkaline phosphatase (ALP) isoenzymes have been characterized in humans. Each isozyme is encoded by a separate gene. Three of them are expressed exclusively in intestine, pla- centa, and germ cells, whereas the fourth isoenzyme is highly expressed in liver, bone, and kidney (L/B/K) and has low expression in other tissues [4]. ALP, a membrane- bound enzyme is anchored to the brush border membrane (BBM) by proteoglycans inositol linkage to phosphatidyl inositol [5]. The physiological function of ALP in most tissues is uncertain, except that the bone isoenzyme has long been thought to play a role in the mineralization of bone and cartilage [6]. Weiss et al. [7] have demonstrated that a mutation in the L/B/K ALP gene that abolishes enzymatic activity causes profound skeletal hypo miner- alization. Further, the presence of the enzyme in matrix vesicles, the sites of early formation of mineral crystallites in cartilage and bone, suggests a role of ALP in minerali- zation [8, 9]. Notably, an inverse relationship has been found between cellular L/B/K ALP expression and tumor aggressiveness [10]. Thus, besides its involvement in bone mineralization, L/B/K ALP could play a role in contrasting osteosarcoma tumor aggressiveness. In addition, the aber- rant expression/activity of L/B/K ALP was observed in seminoma and renal cell carcinoma [11, 12], which could U. Sharma Á D. Pal Á R. Khajuria Á R. Prasad (&) Department of Biochemistry, PGIMER, Chandigarh, India e-mail: fateh1977@yahoo.com S. K. Singh Á A. K. Mandal Department of Urology, PGIMER, Chandigarh, India 123 Mol Cell Biochem (2012) 369:287–293 DOI 10.1007/s11010-012-1391-y