Dipeptidyl peptidase IV (DPPIV) is a multifunctional cell-surface protein that, as well as having dipeptidase activity, is the major binding protein for adenosine deaminase (ADA) and also binds extracellular matrix proteins such as fibronectin and collagen. It typically reduces the activity of chemokines and other peptide mediators as a result of its enzymatic activity. DPPIV is aberrantly expressed in many cancers, and decreased expression has been linked to increases in invasion and metastasis. We asked whether adenosine, a purine nucleoside that is present at increased levels in the hypoxic tumor microenvironment, might affect the expression of DPPIV at the cell surface. Treatment with a single dose of adenosine produced an initial transient (1 to 4 hours) modest (approximately 10%) increase in DPPIV, followed by a more profound (approximately 40%) depression of DPPIV protein expression at the surface of HT-29 human colon carcinoma cells, with a maximal decline being reached after 48 hours, and persisting for at least a week with daily exposure to adenosine. This down-regulation ofDPPIV occurred at adenosine concentrations comparable to those present within the extracellular fluid of colorectal tumors growing in vivo, and was not elicited by inosine or guanosine. Neither cellular uptake of adenosine nor its phosphorylation was necessary for the down-regulation of DPPIV. The decrease in DPPIV protein at the cell surface was paralleled by decreases in DPPIV enzyme activity, binding of ADA, and the ability of the cells to bind to and migrate on cellular fibronectin. Adenosine, at concentrations that exist within solid tumors, therefore acts at the surface of colorectal carcinoma cells to decrease levels and activities of DPPIV. This down-regulation of DPPIV may increase the sensitivity of cancer cells to the tumor-promoting effects of adenosine and their response to chemokines and the extracellular matrix, facilitating their expansion and metastasis.

The level of expression of the chemokine receptor CXCR4 has been shown to play a crucial role in determining the ability of cancer cells to metastasize from the primary tumor and become established in tissue sites that are rich in the CXCR4 ligand CXCL12/SDF-1a. High CXCR4 expression on cancer cells is associated with an increased risk of recurrence and poorer overall survival. We propose that local tissue mediators within the primary tumor or at secondary sites may modulate the level of CXCR4 expression and, therefore, potentially affect the ability of the cancer cells to metastasize. The purine nucleoside adenine-9-b-D-ribofuranoside (adenosine) is generated at high concentrations within the extracellular fluid of solid tumors because of their hypoxia. We show here that adenosine acts through A 2A and A 2B adenosine receptors on human colorectal carcinoma cells to upregulate CXCR4 mRNA expression up to 10-fold and selectively increases cell-surface CXCR4 protein up to 3-fold. This increase in cellsurface CXCR4 enables the carcinoma cells to migrate toward CXCL12, and enhances their proliferation in response to CXCL12. Adenosine may therefore be one of the factors within the tumor microenvironment that facilitates tumor dissemination, by upregulating CXCR4 on certain cancer cells and enhancing cellular responses to CXCL12. ' 2006 Wiley-Liss, Inc.

The insulin receptor substrate (IRS) proteins are cytoplasmic adaptor molecules that function as signaling intermediates downstream of activated cell surface receptors. Based on data implicating IRS-2 but not IRS-1 in breast cancer invasion, survival, and metastasis, we assessed the contribution of IRS-1 and IRS-2 to aerobic glycolysis, which is known to impact tumor growth and progression. For this purpose, we used tumor cell lines derived from transgenic mice that express the polyoma virus middle T antigen (PyV-MT) in the mammary gland and that are wild-type (WT) or null for either Irs-1 (Irs-1 ؊/؊ ) or Irs-2 (Irs-2 ؊/؊ ). Aerobic glycolysis, as assessed by the rate of lactic acid production and glucose consumption, was diminished significantly in Irs-2 ؊/؊ cells when compared with WT and Irs-1 ؊/؊ cells. Expression of exogenous Irs-2 in Irs-2 ؊/؊ cells restored the rate of glycolysis to that observed in WT cells. The transcription factor FoxO1 does not appear to be involved in Irs-2-mediated glycolysis. However, Irs-2 does regulate the surface expression of glucose transporter 1 (Glut1) as assessed by flow cytometry using a Glut1-specific ligand. Suppression of Glut1 expression inhibits Irs-2-dependent invasion, which links glycolysis to mammary tumor progression. Irs-2 was shown to be important for mammalian target of rapamycin (mTor) activation, and Irs-2-dependent regulation of Glut1 surface expression is rapamycin-sensitive. Collectively, our data indicate that Irs-2, but not Irs-1, promotes invasion by sustaining the aerobic glycolysis of mouse mammary tumor cells and that it does so by regulating the mTor-dependent surface expression of Glut1.Glucose metabolism in cancer cells differs significantly from that of normal cells as observed initially by Warburg in the 1920s (1). Specifically, cancer cells depend more on glycolysis than oxidative phosphorylation to generate ATP, even in high oxygen tensions. Subsequent studies have affirmed the importance of aerobic glycolysis in tumor progression and have shown that it provides tumor cells with a selective advantage in their ability to progress toward invasive and metastatic disease (2-4). Significantly, the "Warburg effect" has become a powerful and standard imaging technique for detecting tumors and their metastases by positron emission tomography using [ 18 F]deoxyglucose (5). Aerobic glycolysis is also an ideal target for therapeutic intervention because apoptosis results if this process is perturbed (2, 6). To exploit aerobic glycolysis for the clinical management of cancer, however, much more needs to be learned about how this form of metabolism is induced and sustained in tumors. Our interest is in understanding how aerobic glycolysis is regulated in breast cancer.The insulin receptor substrate (IRS) 3 proteins are cytoplasmic adaptor molecules that function as signaling intermediates downstream of activated cell surface receptors (7). The role of the IRS-2 family member is of particular significance in breast cancer. IRS-2 is predominantly expressed ...

downregulates DPPIV on HT-29 colon cancer cells by stimulating protein tyrosine phosphatase(s) and reducing ERK1/2 activity via a novel pathway.