Activation of tissue plasminogen activator by metastasis-inducing S100P protein

S100P protein in human breast cancer cells is associated with reduced patient survival and, in a model system of metastasis, it confers a metastatic phenotype upon benign mammary tumour cells. S100P protein possesses a C-terminal lysine residue. Using a multiwell in vitro assay, S100P is now shown for the first time to exhibit a strong, C-terminal lysine-dependent activation of tissue plasminogen activator (tPA), but not of urokinase-catalysed plasminogen activation. The presence of 10 μM calcium ions stimulates tPA activation of plasminogen 2-fold in an S100P-dependent manner. S100P physically interacts with both plasminogen and tPA in vitro, but not with urokinase. Cells constitutively expressing S100P exhibit detectable S100P protein on the cell surface, and S100P-containing cells show enhanced activation of plasminogen compared with S100P-negative control cells. S100P shows C-terminal lysine-dependent enhancement of cell invasion. An S100P antibody, when added to the culture medium, reduced the rate of invasion of wild-type S100P-expressing cells, but not of cells expressing mutant S100P proteins lacking the C-terminal lysine, suggesting that S100P functions outside the cell. The protease inhibitors, aprotinin or α-2-antiplasmin, reduced the invasion of S100P-expressing cells, but not of S100P-negative control cells, nor cells expressing S100P protein lacking the C-terminal lysine. It is proposed that activation of tPA via the C-terminal lysine of S100P contributes to the enhancement of cell invasion by S100P and thus potentially to its metastasis-promoting activity

The calcium-binding protein S100P in normal and malignant human tissues

<p>Abstract</p> <p>Background</p> <p>S100P is a Ca²⁺binding protein overexpressed in a variety of cancers, and thus, has been considered a potential tumor biomarker. Very little has been studied about its normal expression and functions.</p> <p>Methods</p> <p>We examined S100P expression in normal human tissues by quantitative reverse transcription polymerase chain reaction and immunohistochemistry. S100P protein expression was also studied in a series of tumors, consisting of 74 ovarian, 11 pancreatic, 56 gastric, 57 colorectal, 89 breast and 193 prostate carcinomas using a novel anti-S100P monoclonal antibody.</p> <p>Results</p> <p>Among the normal tissues, the highest S100P mRNA levels were observed in the placenta and esophagus. Moderate signals were also detected in the stomach, duodenum, large intestine, prostate and leukocytes. At the protein level, the highest reactions for S100P were seen in the placenta and stomach. Immunostaining of tumor specimens showed that S100P protein is expressed in all the tumor categories included in the study, being most prevalent in gastric tumors.</p> <p>Conclusion</p> <p>Based on our observations, S100P is widely expressed in both normal and malignant tissues. The high expression in some tumors suggests that it may represent a potential target molecule for future diagnostic and therapeutic applications.</p

S100P enhances the motility and invasion of human trophoblast cell lines

S100P has been shown to be a marker for carcinogenesis where its expression in solid tumours correlates with metastasis and a poor patient prognosis. This protein’s role in any physiological process is, however, unknown. Here we first show that S100P is expressed both in trophoblasts in vivo as well as in some corresponding cell lines in culture. We demonstrate that S100P is predominantly expressed during the early stage of placental formation with its highest expression levels occurring during the first trimester of gestation, particularly in the invading columns and anchoring villi. Using gain or loss of function studies through overexpression or knockdown of S100P expression respectively, our work shows that S100P stimulates both cell motility and cellular invasion in different trophoblastic and first trimester EVT cell lines. Interestingly, cell invasion was seen to be more dramatically affected than cell migration. Our results suggest that S100P may be acting as an important regulator of trophoblast invasion during placentation. This finding sheds new light on a hitherto uncharacterized molecular mechanism which may, in turn, lead to the identification of novel targets that may explain why significant numbers of confirmed human pregnancies suffer complications through poor placental implantation

Formation of Monomeric S100B and S100A11 Proteins at Low Ionic Strength

The S100 proteins comprise a group of EF-hand proteins that undergo a calcium-induced conformational change allowing them to interact with other proteins and produce a biological response. A unique feature of these proteins is the fact that they can form both homo- and heterodimers independent of calcium binding. The reported dissociation constants for several S100 proteins span a very large range, from 1-4 microM to \u3c\u3c1 nM, suggesting that differing interface surface areas could govern the strength of the binding affinity. In this work, we examine the dimerization mechanism of S100B and S100A11 in the absence of calcium. Using electrospray mass spectrometry, we demonstrate that the monomer-dimer equilibrium in these S100 proteins is strongly dependent on the ionic strength of the solution. At higher ionic strengths (\u3eor=22 mM), both S100A11 and S100B exist predominantly as homodimers. For apo-S100A11, a K(dimer) near 0.01 microM is estimated, while concentration-dependent experiments under these conditions show the K(dimer) for apo-S100B must be even lower. In contrast, lowering the ionic strength results in the formation of monomeric proteins with poorer dimer propensity. For example, the estimated K(dimer) for apo-S100A11 is more than 400 microM at 0.1 mM NH(4)Ac. (1)H-(15)N HSQC NMR experiments in combination with circular dichroism studies show that monomeric S100B and S100A11 proteins are alpha-helical and retain a significant amount of tertiary structure. Our results indicate that apo-S100B has at least a 10-fold stronger propensity to form dimers than does apo-S100A11 in line with a 400 A(2) greater buried surface area for apo-S100B at its dimer interface. These experiments are the first to show that folded monomeric S100 proteins can be isolated, thus paving the way for future experiments aimed at examining the possible role of these monomers in folding and calcium signaling