Chromosome 1p35-36, which encodes
tumor suppressors and mitotic checkpoint control genes, is commonly altered in human
malignancies. One gene at this locus,
stathmin 1 (STMN1), is involved in cell cycle progression and
metastasis. We hypothesized that increased STMN1 expression may play a role in pancreatic neuroendocrine
neoplasm (pNEN)
malignancy. We investigated
stathmin copy number variation,
mRNA, and
protein expression using PCR-Taqman Copy Number Assays, Q-PCR, Western blot, and immunohistochemistry. A mechanistic role for
stathmin in proliferation was assessed in the BON cell line under growth-restrictive conditions and
siRNA silencing. Furthermore, its role in PI3K signaling pathway activation was evaluated using pharmacological inhibitors.
mRNA (p = 0.0001) and
protein (p < 0.05) were overexpressed in pNENs. Expression was associated with pNEN
tumor extension (p < 0.05), size (p < 0.01), and Ki67 expression (p < 0.01). Serum depletion decreased Ki67 expression (p < 0.01) as well as Ser38 phosphorylation (p < 0.05) in BON cells. STMN1 knockdown (
siRNA) decreased proliferation (p < 0.05), and PI3K inhibitors directly inhibited proliferation via
stathmin inactivation (dephosphorylation p < 0.01). We identified that
stathmin was overexpressed and associated with pathological parameters in pancreatic NENs. We postulate that STMN1 overexpression and phosphorylation result in a loss of cell cycle mitotic checkpoint control and may render
tumors amenable to PI3K inhibitory
therapy.