Neurotensin (NT), an intestinal peptide secreted from N cells in the small 
bowel, regulates a variety of physiological functions of the gastrointestinal 
tract, including secretion, gut motility, and intestinal growth. The class IA 
phosphatidylinositol 3-kinase (PI3K) family, which comprised of p110 catalytic 
(α, β and δ) and p85 regulatory subunits, has been implicated in the regulation 
of hormone secretion from endocrine cells. However, the underlying mechanisms 
remain poorly understood. In particular, the role of PI3K in intestinal peptide 
secretion is not known. Here, we show that PI3K catalytic subunit, p110α, 
negatively regulates NT secretion in vitro and in vivo. We demonstrate that 
inhibition of p110α, but not p110β, induces NT release in BON, a human endocrine 
cell line, which expresses NT mRNA and produces NT peptide in a manner analogous 
to N cells, and QGP-1, a pancreatic endocrine cell line that produces NT 
peptide. In contrast, overexpression of p110α decreases NT secretion. 
Consistently, p110α-inhibition increases plasma NT levels in mice. To further 
delineate the mechanisms contributing to this effect, we demonstrate that 
inhibition of p110α increases NT granule trafficking by up-regulating α-tubulin 
acetylation; NT secretion is prevented by overexpression of HDAC6, an α-tubulin 
deacetylase. Moreover, ras-related protein Rab27A (a small G protein) and kinase 
D-interacting substrate of 220 kDa (Kidins220), which are associated with NT 
granules, play a negative and positive role, respectively, in 
p110α-inhibition-induced NT secretion. Our findings identify the critical role 
and novel mechanisms for the PI3K signaling pathway in the control of intestinal 
hormone granule transport and release.