The alpha P-6 integrin is a 140-kDa (nonreduced) laminin receptor. We have
identified a novel 70-kDa (nonreduced) form of the alpha (6) integrin calle
d alpha P-6 for the latin word parvus, meaning small. The variant was immun
oprecipitated from human cells using four different alpha (6)-specific mono
clonal antibodies but not with alpha (3) or alpha (5) antibodies. The alpha
P-6 integrin contained identical amino acid sequences within exons 13-25,
corresponding to the extracellular "stalk region" and the cytoplasmic tail
of the alpha (6) integrin. The light chains of alpha P-6 and alpha P-6 were
identical as judged by alpha (6)A-specific antibodies and electrophoretic
properties. The alpha P-6 variant paired with either beta (1) or beta (4) s
ubunits and was retained on the cell surface three times longer than alpha
(6). Reverse transcription/polymerase chain reaction analysis revealed a si
ngle polymerase chain reaction product. The alpha P-6 variant was found in
human prostate (DU145H, LnCaP, PC3) and colon (SW480) cancer cell lines but
not in normal prostate (PrEC), breast cancer (MCF-7), or lung cancer (H69)
cell lines or a variant of a prostate carcinoma cell line (PC3-N), Protein
levels of alpha P-6 increased 3-fold during calcium-induced terminal diffe
rentiation in a normal mouse keratinocyte model system. A novel form of the
alpha (6) integrin exists on cell surfaces that contains a dramatically al
tered extracellular domain.