Colon-Derived Liver Metastasis,Colorectal Carcinoma,and Hepatocellular Carcinoma Can Be Discriminated by the Ca2+-Binding Proteins S100A6 and S100A11

Background

It is unknown, on the proteomic level, whether the protein patterns of tumors change during metastasis or whether markers are present that allow metastases to be allocated to a specific tumor entity. The latter is of clinical interest if the primary tumor is not known.

Methodology/Principal Findings

In this study, tissue from colon-derived liver metastases (n = 17) were classified, laser-microdissected, and analysed by ProteinChip arrays (SELDI). The resulting spectra were compared with data for primary colorectal (CRC) and hepatocellular carcinomas (HCC) from our former studies. Of 49 signals differentially expressed in primary HCC, primary CRC, and liver metastases, two were identified by immunodepletion as S100A6 and S100A11. Both proteins were precisely localized immunohistochemically in cells. S100A6 and S100A11 can discriminate significantly between the two primary tumor entities, CRC and HCC, whereas S100A6 allows the discrimination of metastases and HCC.

Conclusions

Both identified proteins can be used to discriminate different tumor entities. Specific markers or proteomic patterns for the metastases of different primary cancers will allow us to determine the biological characteristics of metastasis in general. It is unknown how the protein patterns of tumors change during metastasis or whether markers are present that allow metastases to be allocated to a specific tumor entity. The latter is of clinical interest if the primary tumor is not known.     

Photodynamic Therapy-mediated Cancer Vaccination Enhances Stem-like Phenotype and Immune Escape,Which Can Be Blocked by Thrombospondin-1 Signaling through CD47 Receptor Protein

Like most of the strategies for cancer immunotherapy, photodynamic therapy-mediated vaccination has shown poor clinical outcomes in application. The aim of this study is to offer a glimpse at the mechanisms that are responsible for the failure based on cancer immuno-editing theory and to search for a positive solution. In this study we found that tumor cells were able to adapt themselves to the immune pressure exerted by vaccination. The survived tumor cells exhibited enhanced tumorigenic and stem-like phenotypes as well as undermined immunogenicity. Viewed as a whole, immune-selected tumor cells showed more malignant characteristics and the ability of immune escape, which might contribute to the eventual relapse. Thrombospondin-1 signaling via CD47 helped prevent tumor cells from becoming stem-like and rendered them vulnerable to immune attack. These findings prove that the TSP-1/CD47/SIRP-α signal axis is important to the evolution of tumor cells in the microenvironment of immunotherapy and identify thrombospondin-1 as a key signal with therapeutic benefits in overcoming long term relapse, providing new evidence for the clinical promise of cancer vaccination.     

Dephosphorylation of Microtubule Proteins by Brain Protein Phosphatases 1 and 2A, and Its Effect on Microtubule Assembly

Protein phosphatase C was purified 140-fold from bovine brain with 8% yield using histone H1 phosphorylated by the catalytic subunit of cyclic AMP-dependent protein kinase (cyclic AMP-kinase). Brain protein phosphatase C was considered to consist of 10 and 90%, respectively, of the catalytic subunits of protein phosphatases 1 and 2A on the basis of the effects of ATP and inhibitor-2. Protein phosphatase C dephosphorylated microtubule-associated protein 2 (MAP2), tau factor, and tubulin phosphorylated by a multifunctional Ca2+/calmodulin-dependent protein kinase (calmodulin-kinase) and the catalytic subunit of cyclic AMP-kinase. The properties of dephosphorylation of MAP2, tau factor, and tubulin were compared. The Km values were in the ranges of 1.6-2.7 microM for MAP2 and tau factor. The Km value for tubulin decreased from 25 to 10-12.5 microM in the presence of 1.0 mM Mn2+. No difference in kinetic properties of dephosphorylation was observed between the substrates phosphorylated by the two kinases. Protein phosphatase C did not dephosphorylate the native tubulin, but universally dephosphorylated tubulin phosphorylated by the two kinases. The holoenzyme of protein phosphatase 2A from porcine brain could also dephosphorylate MAP2, tau factor, and tubulin phosphorylated by the two kinases. The phosphorylation of MAP2 and tau factor by calmodulin-kinase separately induced the inhibition of microtubule assembly, and the dephosphorylation by protein phosphatase C removed its inhibitory effect. These data suggest that brain protein phosphatases 1 and 2A are involved in the switch-off mechanism of both Ca2+/calmodulin-dependent and cyclic AMP-dependent regulation of microtubule formation.     

SOI1 Encodes a Novel, Conserved Protein That Promotes TGN–Endosomal Cycling of Kex2p and Other Membrane Proteins by Modulating the Function of Two TGN Localization Signals

Localization of yeast Kex2 protease to the TGN requires a signal (TLS1) in its cytosolic tail (C-tail). Mutation of TLS1 results in rapid transit of Kex2p to the vacuole. Isolation of suppressors of the Tyr₇₁₃Ala mutation in TLS1 previously identified three SOI genes. SOI1, cloned by complementation of a sporulation defect, encodes a novel, hydrophilic 3,144-residue protein with homologues in Caenorhabditis elegans, Drosophila melanogaster, and humans. Epitope-tagged Soi1p existed in a detergent-insensitive, sedimentable form. Deletion of SOI1 impaired TGN localization of wild-type Kex2p and a fusion protein containing the C-tail of Ste13p, and also caused missorting of carboxypeptidase Y and accelerated vacuolar degradation of the Vps10p sorting receptor. Deletion of SOI1 improved retention of Tyr₇₁₃Ala Kex2p in the pro-α-factor processing compartment but, unlike the original soi1 alleles, did not increase the half-life of Tyr₇₁₃Ala Kex2p. These results suggested that Soi1p functions at two steps in the cycling of Kex2p and other proteins between the TGN and prevacuolar compartment (PVC). This hypothesis was confirmed in several ways. Soi1p was shown to be required for optimal function of TLS1. Suppression of the Tyr₇₁₃Ala mutation by mutation of SOI1 was shown to be caused by activation of a second signal (TLS2) in the Kex2p C-tail. TLS2 delayed exit of Kex2p from the TGN, whereas TLS1 did not affect this step. We propose that Soi1p promotes cycling of TGN membrane proteins between the TGN and PVC by antagonizing a TGN retention signal (TLS2) and facilitating the function of a retrieval signal (TLS1) that acts at the PVC.     

Mutations in Intracellular Loops 1 and 3 Lead to Misfolding of Human P-glycoprotein (ABCB1) That Can Be Rescued by Cyclosporine A,Which Reduces Its Association with Chaperone Hsp70

P-glycoprotein (P-gp) is an ATP binding cassette transporter that effluxes a variety of structurally diverse compounds including anticancer drugs. Computational models of human P-gp in the apo- and nucleotide-bound conformation show that the adenine group of ATP forms hydrogen bonds with the conserved Asp-164 and Asp-805 in intracellular loops 1 and 3, respectively, which are located at the interface between the nucleotide binding domains and transmembrane domains. We investigated the role of Asp-164 and Asp-805 residues by substituting them with cysteine in a cysteine-less background. It was observed that the D164C/D805C mutant, when expressed in HeLa cells, led to misprocessing of P-gp, which thus failed to transport the drug substrates. The misfolded protein could be rescued to the cell surface by growing the cells at a lower temperature (27 °C) or by treatment with substrates (cyclosporine A, FK506), modulators (tariquidar), or small corrector molecules. We also show that short term (4–6 h) treatment with 15 μm cyclosporine A or FK506 rescues the pre-formed immature protein trapped in the endoplasmic reticulum in an immunophilin-independent pathway. The intracellularly trapped misprocessed protein associates more with chaperone Hsp70, and the treatment with cyclosporine A reduces the association of mutant P-gp, thus allowing it to be trafficked to the cell surface. The function of rescued cell surface mutant P-gp is similar to that of wild-type protein. These data demonstrate that the Asp-164 and Asp-805 residues are not important for ATP binding, as proposed earlier, but are critical for proper folding and maturation of a functional transporter.