1A) and failure of APLP2 reduction (by siRNA or ��-secretase inhibitors) to enhance APP C-terminal cleavage (data not shown). Selective cleavage of APLP2 over APP can arise through secretase specificity, intracellular compartmentalization, APLP2-APP homo- or hetero-oligomerization and/or isoforms of APLP2 citation or APP expressed (58�C63). Full-length APLP2 and APP are capable of forming homo- or hetero-oligomers, which may be disrupted upon soluble APLP2 or soluble APP binding (57,65�C67). The transmembrane-soluble complexes formed by APLP2 and APP are significant because the activity of APLP2 and APP receptors depends upon the complex formed. For example, dimers of full-length APP have been proposed to activate cell death in neuronal cells, where full-length APP-soluble APP dimers disrupt the cytotoxic signal (67).

While in our experiments protein expression of APLP2 or APP was not altered following loss of the other family member, alterations to additional regulatory mechanisms of APLP2 and/or APP may occur. Future investigations are required to explore the possibilities of altered APLP2 or APP regulatory mechanisms and to dissect functional identities of APLP2 and APP in pancreatic cancer growth and viability. Treatment with ��-secretase inhibitors caused not only a decrease in APLP2 C-terminal fragments, but also a reduction in S2-013 cell viability (Fig. 3). Our data indicate that inhibitory therapies that target APLP2, APP and BACE may be promising for the treatment of pancreatic cancer.

Notably, tolfenamic acid, which is currently under investigation for use in pancreatic cancer (68�C71), has been shown to impair expression of APP and BACE (72). Reduced cleavage of other proteins (in addition to APLP2) might also contribute to the ability of the ��-secretase inhibitors to affect pancreatic cancer cell viability. The ��-secretase Cilengitide inhibitors target ��-secretases that cleave APP as well as APLP2. However, our analysis has not shown a very high expression of APP C-terminal fragments in pancreatic cancer cell lines except BxPC3 (Fig. 1). Cleavage of additional proteins (not in the APP/APLP2 family) able to influence viability may be affected by the ��-secretase inhibitors. BACE2 substrate proteins are not well defined, although there is somewhat more information on BACE1 substrates, which include heregulins (73�C75). Heregulin proteins have been noted to be over-expressed in pancreatic cancer cells and to influence their growth (76). Thus, heregulins might have a role in ��-secretase inhibitor-mediated reduction of pancreatic cancer cell viability.