S100PBP (S100P binding protein)

Description	There are two different transcript variants of S100PBP. Variant 1 is 4317 base pairs and contains 7 exons. Variant 2 is 1483 base pairs and also contains 7 exons. This is shown in the above alignment. The coding sequence for each isoform is indicated in red, with the non-coding sequence in grey. Unmatched base pairs between the two isoforms are highlighted in green and the position of a missing CAG codon in isoform B is circled. The end of the isoform B sequence is indicated by a bold line.

Description	S100PBP isoform A codes for a 45 kDa protein and isoform B for 37 kDa protein. Secondary structure analysis of the S100PBP protein sequence was performed using the secondary structure consensus prediction tool (NPS@, Lyon, France). Based on three different methods: DSC (Discrimination of protein Secondary structure Class), MLRC (Multivariate Linear Regression Combination) and PHD neural network system, S100PBP was shown to be largely unstructured and unfolded, as seen above ("h" represents a helix, "c" a coil and "e" an extended strand).
Expression	S100PBP is expressed in various normal tissues including prostate and lung and in both the endocrine and exocrine pancreas. S100PBP is also expressed in malignant tissues such as liver hepatocellular carcinoma and thyroid carcinoma (Lines et al., 2012). In pancreas, S100PBP is expressed in decreasing levels as cancer develops and progresses, which is an inverse pattern of expression of its binding partner, S100P. This is shown on picture below (a= acinar cells, d= ducts; PanIN= pancreatic intraepithelial neoplasia, a precursor lesion to pancreatic cancer, black arrows= PanIN-1, red arrows= PanIN-2; PDAC= pancreatic cancer).
Localisation	Predominantly nuclear.
Function	The exact functions of S100PBP are currently unknown, however it has been shown that S100PBP can bind to the metastasis related protein S100P (Dowen et al., 2005).
Homology	No homology to any currently described protein is seen.

Note
Entity	Pancreatic ductal adenocarcinoma (PDAC)
Note	Overexpression of S100PBP in FA6 pancreatic cancer cells that show low levels of endogenous S100PBP expression and silencing of S100PBP in MiaPaCa2 cells (high levels of endogenous S100PBP) showed no effect on proliferation or wound healing. While cell migration was not affected in majority of tested pancreatic cancer cell lines after modulation of S100PBP expression, significant changes in invasion (increase in MiaPaCa2 and Panc1 cells after S100PBP silencing and decrease in RwP1 cells after overexpression) were seen. However, the most affected cellular function after modulation of S100PBP expression was adhesion. Loss of S100PBP causes an increase in pancreatic cancer cell adhesion to extracellular matrix proteins which was mediated by cysteine protease Cathepsin Z (CTSZ) and the integrin ανβ5 (Lines et al., 2012). Schematic and simplified diagram of the putative mechanism behind S100PBP mediated changes in pancreatic cell adhesion is shown below: in normal cells where S100PBP is highly expressed, low levels of CTSZ are present; no or very little ανβ5 is seen on the cellular surface. In cancer cells (PDAC), S100PBP levels decrease, which results in an increase in CTSZ expression; CTSZ is then secreted and can interact with ανβ5, promoting thus the adhesion.
Disease	Pancreatic cancer.

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