Distinct expression of C4.4A in colorectal cancer detected by different antibodies

The metastasis-associated gene C4.4A encodes a glycolipid-anchored membrane protein expressed in several human malignancies. The present study aimed to perform a detailed assessment of C4.4A expression in colorectal cancer tissues, in terms of intra-cellular localization, intra-tumoral location and difference in molecular weight. To advance this goal, we developed three new antibodies against the C4.4A protein (two polyclonal Abs: C4.4A-119 and C4.4A-277 and one monoclonal Ab: C4.4A GPI-M) to use in addition to the two previously produced polyclonal Abs (C4.4A-81, C4.4A GPI-P). Antibody specificities were confirmed by absorption tests. Western blot analysis and immunohistochemistry showed that the C4.4A-119 and C4.4-277 Abs detected 70-kDa C4.4A, mainly in the cytoplasm, irrespective of intra-tumoral location. The C4.4A GPI-P and C4.4A GPI-M Abs reacted with the membranous ~40-kDa C4.4A, exclusively at the tumor invasive front, and each detected an identical tumor cell population. The tested antibodies showed varied C4.4A detection rates in 33 CRC tissues. The C4.4A-277 Ab yielded the highest positive rate in 29 of 33 CRC tissues (87.9%), while the C4.4A GPI-P and C4.4A GPI-M Abs each only showed 33.3% positivity. The present findings suggest that the GPI anchor signaling sequence may be essential for detecting membranous C4.4A at the invasive front of CRC tissues.