The Calcium-binding Protein S100A2 Interacts with p53 and Modulates Its Transcriptional Activity

Expression of calcium-binding proteins S100A2 and S100A4 in Barrett's adenocarcinomas

In this study, we investigated the mRNA and protein expression of S100A2 and S100A4 in adenocarcinomas of the stomach and esophagus. Real-time reverse transcription-polymerase reaction analysis on 72 tumors revealed frequent overexpression of S100A2 and S100A4 in Barrett's adenocarcinomas (BAs) (P < .01). Immunohistochemical analysis on tumor tissue microarrays that contained 187 tumors showed absent to weak staining for S100A2 in all normal gastric mucosa samples, whereas normal esophageal mucosa samples demonstrated moderate to strong nuclear staining. Contrary to the nuclear expression of S100A2 in normal esophageal mucosa, two thirds of Barrett's dysplasia and BAs that overexpressed S100A2 demonstrated stronger cytosolic staining than nuclear staining (P < .001). Overexpression of S100A2 protein was more frequently seen in well-differentiated tumors than in others (P = .02). Moderate to strong staining of S100A4 was detected in two thirds of tumors and was frequently observed in the presence of Barrett's esophagus (P = .02). Similar to S100A2, the expression of S100A4 was predominantly cytosolic in two thirds of the tumors (P = .001). There was a significant correlation between S100A4 overexpression and lymph node metastasis (N(2)-N(4)) (P = .027). These results demonstrate frequent cytosolic overexpression of S100A2 and S100A4 in BAs. Further studies are ongoing to understand the biological significance of these S100A proteins in Barrett's tumorigenesis.

Purification and crystallization of the human EF-hand tumour suppressor protein S100A2

S100A2 is a Ca(2+)-binding EF-hand protein that is mainly localized in the nucleus. There, it acts as a tumour suppressor by binding and activating p53. Wild-type S100A2 and a S100A2 variant lacking cysteines have been purified. CD spectroscopy showed that there are no changes in secondary-structure composition. The S100A2 mutant was crystallized in a calcium-free form. The crystals, with dimensions 30 x 30 x 70 microm, diffract to 1.7 A and belong to space group P2(1)2(1)2(1), with unit-cell parameters a = 43.5, b = 57.8, c = 59.8 A, alpha = beta = gamma = 90 degrees. Preliminary analysis of the X-ray data indicates that there are two subunits per asymmetric unit.

Estrogen receptor-beta regulates psoriasin (S100A7) in human breast cancer

We have previously observed a paradoxical relationship of the psoriasin/S100A7 gene with estrogen response in-vitro in ERalpha positive cells but its association with ERalpha negative status in-vivo raising the possibility that S100A7 might be regulated by ERbeta in breast cancer. Using doxycycline-inducible ERbeta and ERalpha expressing MCF-7 cells the hypothesis that psoriasin/S100A7 is ERbeta regulated was investigated To explore the relationship between psoriasin/S100A7 and ERbeta expression in-vivo, we also assessed a cohort of 233 ERalpha negative breast tumors using tissue microarrays and immunohistochemistry. Psoriasin/S100A7 was increased by 17beta-estradiol (E2) following ERbeta induction, in several clones of ERbeta over-expressing but not in the original MCF-7 cells, nor clones over-expressing ERalpha. The effect of E2 on psoriasin/S100A7 was inhibited by 4-hydroxytamoxifen and ICI 182780 but not with a selective ERalpha antagonist. An ERbeta selective-agonist but not an ERalpha selective-agonist, induced psoriasin/S100A7. This induction still occurred after stable down-regulation of ERalpha using siRNA in ERbeta inducible cells. E2 increased psoriasin/S100A7 mRNA but cycloheximide treatment inhibited this effect. A relationship between ERbeta and psoriasin/S100A7 was observed in the p53 immunohistochemically negative subset of invasive breast tumors in-vivo (r = 0.225, p = 0.046, n = 79). In conclusion we demonstrate that E2 induction of psoriasin/S100A7 can be specifically regulated through ERbeta in-vitro and associated with ERbeta in-vivo. These data support the hypothesis that psoriasin/S100A7 is specifically regulated by ERbeta activity and could be useful to guide future therapies targeting ERbeta in certain phenotypic subsets of breast cancers in-vivo.

Cyclooxygenase-2 Is Involved in S100A2-Mediated Tumor Suppression in Squamous Cell Carcinoma

S100A2 is considered a putative tumor suppressor due to its loss or down-regulation in several cancer types. However, no mechanism has been described for the tumor suppressor role of S100A2. In this study, ectopic expression of S100A2 in the human malignant squamous cell carcinoma cell line KB resulted in a significant inhibition of proliferation, migration, and invasion. Moreover, S100A2 significantly reduced the number of colonies (>or=0.5 mm) formed in semisolid agar and decreased tumor growth and burden in nude mice. cDNA microarray analysis was used to compare mRNA expression profiles of vector- and S100A2-expressing isogenic cells. Among the genes deregulated by S100A2, the expression of cyclooxygenase-2 (COX-2) mRNA was significantly suppressed by S100A2 (2.4-fold). Western blot analysis confirmed that S100A2 reduced the expression of COX-2 protein in stably and transiently transfected KB and RPMI-2650 cells. COX-2 is frequently overexpressed in various types of cancer and plays an important role in tumor progression. Partial restoration of COX-2 expression attenuated the antitumor effect of S100A2 both in vitro and in vivo. Although the interplay between S100A2 and COX-2 remains to be clarified, these findings first showed a potent antitumor role of S100A2 in squamous cell carcinoma partly via reduced expression of COX-2.

Copper binding affinity of S100A13, a key component of the FGF-1 nonclassical copper-dependent release complex

S100A13 is a member of the S100 protein family that is involved in the copper-dependent nonclassical secretion of signal peptideless proteins fibroblast growth factor 1 and interleukin 1 lpha. In this study, we investigate the effects of interplay of Cu2+ and Ca2+ on the structure of S100A13 using a variety of biophysical techniques, including multi-dimensional NMR spectroscopy. Results of the isothermal titration calorimetry experiments show that S100A13 can bind independently to both Ca2+ and Cu2+ with almost equal affinity (Kd in the micromolar range). Terbium binding and isothermal titration calorimetry data reveal that two atoms of Cu2+/Ca2+ bind per subunit of S100A13. Results of the thermal denaturation experiments monitored by far-ultraviolet circular dichroism, limited trypsin digestion, and hydrogen-deuterium exchange (using 1H-15N heteronuclear single quantum coherence spectra) reveal that Ca2+ and Cu2+ have opposite effects on the stability of S100A13. Binding of Ca2+ stabilizes the protein, but the stability of the protein is observed to decrease upon binding to Cu2+. 1H-15N chemical shift perturbation experiments indicate that S100A13 can bind simultaneously to both Ca2+ and Cu2+ and the binding of the metal ions is not mutually exclusive. The results of this study suggest that the Cu2+-binding affinity of S100A13 is important for the formation of the FGF-1 homodimer and the subsequent secretion of the signal peptideless growth factor through the nonclassical release pathway.

Calcium-dependent and -independent interactions of the S100 protein family

The S100 proteins comprise at least 25 members, forming the largest group of EF-hand signalling proteins in humans. Although the proteins are expressed in many tissues, each S100 protein has generally been shown to have a preference for expression in one particular tissue or cell type. Three-dimensional structures of several S100 family members have shown that the proteins assume a dimeric structure consisting of two EF-hand motifs per monomer. Calcium binding to these S100 proteins, with the exception of S100A10, results in an approx. 40 degrees alteration in the position of helix III, exposing a broad hydrophobic surface that enables the S100 proteins to interact with a variety of target proteins. More than 90 potential target proteins have been documented for the S100 proteins, including the cytoskeletal proteins tubulin, glial fibrillary acidic protein and F-actin, which have been identified mostly from in vitro experiments. In the last 5 years, efforts have concentrated on quantifying the protein interactions of the S100 proteins, identifying in vivo protein partners and understanding the molecular specificity for target protein interactions. Furthermore, the S100 proteins are the only EF-hand proteins that are known to form both homo- and hetero-dimers, and efforts are underway to determine the stabilities of these complexes and structural rationales for their formation and potential differences in their biological roles. This review highlights both the calcium-dependent and -independent interactions of the S100 proteins, with a focus on the structures of the complexes, differences and similarities in the strengths of the interactions, and preferences for homo- compared with hetero-dimeric S100 protein assembly.

Recent advances in Ca2+-dependent Ras regulation and cell proliferation

Our understanding of the mechanisms whereby growth factors stimulate cell proliferation through the Ras pathway stems largely from studies of the canonical pathway involving recruitment of Ras activators and inhibitors to the vicinity of receptor tyrosine kinases via phosphotyrosine-binding adaptor proteins. Ca(2+) has seldom joined the party, despite the identification of phospholipase Cgamma and Ca(2+) entry as receptor tyrosine kinase-dependent signals. Mechanisms by which Ca(2+) can directly influence Ras activity have remained relatively elusive. Similarly, the mechanisms whereby Ca(2+) modulates the cell cycle have been equally murky, and yet there are some interesting parallels in the role of Ras and Ca(2+) in cell cycle re-entry. This review focuses on a number of novel mechanisms that link Ca(2+) with the regulation of Ras activity and signaling output. Their collective discovery adds to the complexities of Ras regulation and raises further questions about the role of Ca(2+) signals in Ras-dependent cell proliferation.

Differential expression of S100A2 and S100A4 in lung adenocarcinomas: clinicopathological significance, relationship to p53 and identification of their target genes

Previous studies suggest that some S100 proteins are involved in the progression of certain types of cancer. However, no comprehensive data is currently available on the expression of S100 family genes in lung adenocarcinomas. Oligonucleotide array, quantitative reverse transcription-polymerase chain reaction and western blot analyses of lung adenocarcinoma cell lines and bronchiolar epithelial cells (SAEC and NHBE) revealed that S100A2 and S100A4 were the most strikingly downregulated and upregulated members of the S100 family, respectively. Immunohistochemical analyses of 94 primary lung adenocarcinomas showed that positive S100A2 expression (33/94, 35.1%) was significantly associated with lymphatic invasion (P=0.0233) and positive S100A4 expression (19/94, 20.2%) with vascular invasion (P=0.0454). Interestingly, a strong inverse relationship was found between S100A4 and p53 expression (P=0.0008). Survival analyses showed that S100A4 positivity was associated with poor patient prognosis (P=0.042). S100A2 positivity was not associated with patient survival when the whole patient group was analyzed; however, S100A2 positivity was a favorable prognostic indicator in patients with p53-negative tumors (P=0.0448). Finally, we used oligonucleotide array analyses and identified potential S100A2 and S100A4 target genes involved in cancer progression: S100A2 induced RUNX3 and REPRIMO; S100A4 induced EZRIN, RUNX1 and WISP1; S100A2 repressed EGFR, NFKB2 and RELA2; and S100A4 repressed ANXA10 and IL1RN. Thus, the present study demonstrates involvement of S100A2 and S100A4 in the progression of lung adenocarcinomas and an inverse association between S100A4 and p53 expression, and provides a list of targets regulated by S100A2 and S100A4.