PTEN and neoplasm: Although multiple proteins with diverse biological functions including tumor suppressors such as APC, PTEN, or cell polarity proteins such as Par-3, aPKCλ are localized at the tight junction location, it was only in the late 1980s that biochemical and immunolocalization studies identified the 225 kDa protein zonula occludens-1 (Z0-1) as the first polypeptide exclusively associated with the TJ [26].