The Ras association domain (RASSF) proteins are named due to the presence of a Ras association (RA) domain in their N or C terminus that can potentially interact with the Ras GTPase family of proteins. These GTPases control a variety of cellular processes, such as membrane trafficking, apoptosis, and proliferation. RASSF proteins contain several other functional domains that modulate associations with other proteins. RASSF proteins with the RA domain at the C terminus (which are termed C-terminal or classical RASSF) usually also include a Salvador-RASSF-Hippo (SARAH) domain involved in several protein-protein interactions and for homo- and heterodimerisation of RASSF isoforms. N-terminal RASSF proteins (with the RA domain in the N terminus) do not usually contain a SARAH domain [].At least 10 RASSF family members have been characterised (with multiple splice variants), many of which have been shown to play a role in tumour suppression. RASSF proteins also act as scaffolding agents in microtubule stability, regulate mitotic cell division, control cell migration and cell adhesion, and modulate NF-KB activity and the duration of inflammation. Loss of RASSF expression through promoter methylation has been shown in numerous types of cancer, including leukemia, melanoma, breast and prostate cancer [].RASSF9 is one of the N-terminal RASSF proteins, characterised by an RA domain in the N terminus. It was previously called P-CIP1 (peptidylglycine alpha-amidating monooxygenase (PAM) COOH-terminal interactor protein-1), and was believed to play a role in the regulation of PAM in endosomal pathways []. Very little else is known about the function of RASSF9, but it has been suggested to be involved in epidermal homeostasis [].
