|M.Sc Thesis||Department of Medicine|
|Prof. Neufeld Gera|
Neuropilin-1 and -2 (NP) are transmembrane proteins which play important roles in axonal growth via the binding of semaphorins (Sema), and in angiogenesis through binding of VEGF. Previously we found that NP-2 is specifically expressed in pancreatic islets and in gastrointestinal (GI) neuroendocrine (NE) cells and by the vast majority of pancreatic NE tumors (PNTs).
A primary goal of this study was to validate an in-vitro model in which to explore NPs function in islet cell physiology. We first examined NP expression in the pluripotential rat AR42J cell-line. Although NE differentiation was induced no NP-2 expression was detectable. The second cell-line studied was the rat INS cell-line. Expression of NP-2, NP-1, Sema-3F and 3A was confirmed by RT-PCR. 125I-VEGF165 bound INS cells and formed complexes with NP. In conclusion, INS cells are suitable for exploring NP’s role in islet physiology.
Previously, NP-2 expression in islet cells was detected by immunohistochemistry (IHC). Here we validated expression of NP-2 mRNA in the rat pancreas and intestine by RT-PCR and Northern blot. Expression of NP-1, Sema-3A and 3F mRNA was also detected. Double-IHC staining experiments revealed that NP-1 was specifically expressed in pancreatic a -cells, whereas Sema 3A was expressed in b-cells.
NP-2 is both a sensitive and specific IHC marker for PNTs. Here we showed that NP-1 and Sema-3A are both sensitive markers for PNTs regardless of their hormonal subtype. Expression of NP-2 was not found in other NE cells except for those of the GI tract. In contrast, expression of NP-1 and Sema-3A was detected in a number of other NE tissues and in their malignant counterparts.
In summary, NPs and their Sema ligands are expressed by specific pancreatic islet cells and may be used as sensitive IHC markers for PNTs although only NP-2 is specific. The role of NP and Sema in islet cell physiology or tumorogenesis remains to be elucidated.