SSTR5 P335L monoclonal antibody differentiates pancreatic neuroendocrine neuroplasms with different SSTR5 genotypes

Abstract

Background Somatostatin receptor type 5 (SSTR5) P335L is a hypofunctional single nucleotide polymorphism of SSTR5 with implications in tumor diagnostics and therapy. The purpose of this study is to determine whether a SSTR5 P335L-specific monoclonal antibody (mAb) could sufficiently differentiate pancreatic neuroendocrine tumor (PNT) patients with different SSTR5 genotypes. Methods Cellular proliferation rate, SSTR5 mRNA level and SSTR5 protein level were measured by performing MTS assay, qRT-PCR and western blotting and immunohistochemistry, respectively. SSTR5 genotype was determined with the TaqMan SNP Genotyping assay. Results 1) SSTR5 analogue RPL-1980 inhibited cellular proliferation of CAPAN-1 cells more significantly than that of PANC-1 cells. 2) Only PANC-1 (TT) cells, but not CAPAN-1 (CC) cells expressed SSTR5 P335L. 3) In 29 Caucasian PNT patients, 38% had TT genotype for SSTR5 P335L, 24% had CC genotype for WT SSTR5, and 38% had CT genotype for both SSTR5 P335L and WT SSTR5. 4) Immunohistochemistry using SSTR5 P335L mAb detected immunostaining signals only from the PNT specimens with TT and CT genotypes, but not those with CC genotypes. Conclusions A SSTR5 P335L mAb that specifically recognizes SSTR5 P335L, but not WT SSTR5, could differentiate PNT patients with different SSTR5 genotypes, thus providing a potential tool for clinical diagnosis of PNT.

Down-regulation of pancreatic and duodenal homeobox-1 by somatostatin receptor subtype 5: a novel mechanism for inhibition of cellular proliferation and insulin secretion by somatostatin

“…Among them, SSTR5 P335L is a non-synonymous SNP resulting from a C to T change at the 1004th nucleotide of the human SSTR5 gene (Zhou et al, 2011c ). The SNP widely exists in the human population and in patients with pancreatic cancer (Li et al, 2011 ; Zhou et al, 2011c ) and pancreatic neuroendocrine tumors (Zhou et al, 2011b ), which are race-dependent. SSTR5 P335L acts as a hypofunctional SNP since SSTR5 P335L enhances cell proliferation in contrast to wild-type SSTR5 (Zhou et al, 2011c ).…”

“…SSTR5 knockout mice develop islet neoplasia associated with enlarged islets (Wang et al, 2004 , 2005a , b ). Due to its differential expression, SSTR5 is involved in tumorigenesis and drug responsiveness of a variety of human cancers including pancreatic cancer (Reubi et al, 1988 ; Li et al, 2011 ; Zhou et al, 2011a ; Kaemmerer et al, 2013 ), pancreatic endocrine tumors (PETs) (Zhou et al, 2011b , 2012 ; Kaemmerer et al, 2013 ), pulmonary neuroendocrine tumors (Tsuta et al, 2012 ), gastroenteropancreatic neuroendocrine tumors (Kim et al, 2011a ; Sclafani et al, 2011 ), small cell lung cancer (Oddstig et al, 2011 ), gallbladder cancer (Guo et al, 2013 ), colon cancer (Wang et al, 2013 ), endocrine pituitary tumors (Nishioka et al, 2011 ; Mayr et al, 2013 ; Chinezu et al, 2014 ), thyroid cancer (Ocak et al, 2013 ), corticotroph adenomas (Fleseriu and Petersenn, 2013 ), prostate cancer (Gu et al, 2010 ; Mazzucchelli et al, 2011 ; Lattanzio et al, 2013 ), and breast cancer (Gu et al, 2010 ). SSTR5 is also involved in the regulation of angiogenesis (Zatelli et al, 2001 ) and apoptosis (Qiu et al, 2006 ; Wang et al, 2013 ).…”

Notch1 Activation Up-Regulates Pancreatic and Duodenal Homeobox-1

“…Rabbit anti-goat IgG was obtained from Zymed Laboratories Inc. (South San Francisco, CA, USA). PNET specimens were as previously described [ 58 ].…”