Niemann-Pick Type C2 (NPC2) plays an important role in the regulation of intracellular
cholesterol homeostasis via direct binding with free
cholesterol. However, little is known about the significance of NPC2 in
cancer. In this study, we have pinpointed the impact of various different
cancers on NPC2 expression. A series of anti-NPC2
monoclonal antibodies (mAbs) with the
IgG2a isotype were generated and
peptide screening demonstrated that the reactive
epitope were
amino acid residues 31-40 of the
human NPC2 protein. The specificity of these mAbs was confirmed by Western blotting using
shRNA mediated knock-down of NPC2 in human SK-Hep1 cells. By immunohistochemical staining, NPC2 is expressed in normal kidney, liver, breast, colon, lung, esophageal, uterine cervical, pancreatic and stomach tissue. Strong expression of NPC2 was found in the distal and proximal convoluted tubule of kidney and the hepatocytes of liver. Normal esophageal, uterine cervical, pancreatic, stomach, breast, colon and lung tissue stained moderately to weakly. When compared to their normal tissue equivalents, NPC2 overexpression was observed in
cancers of the breast, colon and lung. Regarding to
breast cancer, NPC2 up-regulation is associated with
estrogen receptor (-),
progesterone receptor (-) and human
epidermal growth factor receptor (+). On the other hand, NPC2 was found to be down-regulated in
renal cell carcinoma,
liver cirrhosis and
hepatoma tissues. By
antigen-capture
enzyme immunoassay ELISA, the serum NPC2 is increased in patients with
cirrhosis and
liver cancer. According to western blot data, the change of glycosylated pattern of NPC2 in serum is associated with
cirrhosis and
liver cancer. To the best of our knowledge, this is the first comprehensive immunohistochemical and serological study investigating the expression of NPC2 in a variety of different human
cancers. These novel
monoclonal antibodies should help with elucidating the roles of NPC2 in
tumor development, especially in liver and breast
cancers.