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ALBERTO BARTOLOMÉ Y COLS. AN. R. ACAD. NAC. FARM.

tein synthesis and folding, which in turn makes them extremely
prone to misfolded protein accumulation (17). Moreover, mTORC1
regulates the autophagic activity of the cell, which has proved to be
essential for ß cell homeostasis (18).

Just recently, animal models have shown the key role of TSC1-
TSC2 complex in pancreatic ß cells. Specific disruption of the com-
plex in ß cells by either TSC1 (19), TSC2 deletion (20, 21) or Rheb
overexpression (22), results in hyperinsulinemia and improved glu-
cose tolerance mainly due to an increase in ß cell size.

Alternative splicing of the IR (insulin receptor) results in two
isoforms, one encoding the 36 nucleotide exon 11 (IRB) and the
other one without it (IRA) (23). The relative expression of the two
isoforms varies among different tissues (24), and may play a role
in different pathological conditions such as cancer or insulin resist-
ance (25). We have recently observed an increase of IRA in pancre-
atic islets from inducible-liver IR knock-out (iLIRKO) mice show-
ing compensatory ß cell hyperplasia in response to hepatic insulin
resistance (26).

Here, we report a differential regulation of TSC2 phosphorylation
and mTORC1 signaling by insulin, glucose, or energetic status in pan-
creatic ß cell lines. Also are described its consequences on prolifera-
tion, and the involvement of autophagy or ER stress in ß cell death
or survival.

2. MATERIALS AND METHODS

2.1. Antibodies and reagents

All antibodies were from Cell Signaling Biotechnology unless stat-
ed otherwise. Exceptions were IR-ß (Santa Cruz), TSC1 (Bethyl
Laboratories), P-mTOR Ser2448 (Biosource), ß-actin (Sigma), anti-
mono and poly-ubiquitinated protein conjugates FK2 mAb (Enzo Life
Sciences). Antibody against P-TSC2 Ser664 used for Western-blot was
a generous gift from P.P. Pandolfi (Beth Israel Deaconess Medical
Center, Boston, MA). Chemicals were from Calbiochem (U0126, wort-
mannin and rapamycin) or Sigma-Aldrich.

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