Trp53, iNOS and lymphomas—NO easy answer
It is estimated that about 50% of all human cancers are related to p53 dysfunction; therefore, studies on tumor development inTrp53 (murine p53) deficient mice have been very important. Interestingly, these mice spontaneously develop lymphomas of mainly thymic origin.
NOS (Nitric oxide synthase) and its inducible form iNOS produce NO. Various studies have linked an interaction between p53 and iNOS in cancer. For this reason, Tatemichi et al. hypothesized that Trp53-deficient mice that also lacked iNOS would have a decreased incidence of tumor occurrence.
On pages 819–828, Tatemichi and colleagues describe a thorough set of experiments in which they examined the consequence of iNOS deficiency in all genotypic variations of Trp53 mutant mice.
The absence of iNos reduced the incidence of thymic lymphoma by 40% and 90% in Trp53-/- and Trp53+/- mice, respectively. What was very surprising, however, was that mice deficient in iNOS showed an increased occurrence of non-thymic lymphomas: 51% in Trp53-/-iNOS-/- compared to 29% in Trp53-/-iNOS+/+. In contrast to the non-thymic lymphomas of B cell origin that have been previously characterized in Trp53-/- mice, Trp53-/-iNOS-/- mice had non-thymic lymphomas with a T-cell lineage. Overexpression of Th2 cytokines, most notably IL-10, was demonstrated by RT-PCR in Trp53-/ and Trp53+/- iNOS-deficient animals. IL-10 expression also correlated with Bcl-2. Interestingly it has been shown previously that IL-10 can rescue T-cell apoptosis via up-regulation of Bcl-2.
These studies demonstrated that, in contrast to what the authors had previously assumed, iNOS can have a protective effect in the context of p53 deficiency but this does differ in various lymphoid organs.
A Saving Kiss in Gastric Cancer
Gastric carcinoma is a very aggressive disease with a high metastatic potential and a very poor prognosis. KiSS-1 is a recently discovered tumor suppressor gene candidate and an inhibitory molecule in metastasis. The precise mechanism of how KiSS-1 could exert its anti-metastatic effect remains unknown.
In this elegant study reported on pages 868–872, Dhar et al. examined the potential influence of KiSS-1 expression on the phenotype and outcome of gastric cancer. Tumor and normal tissue were taken from 40 gastric cancer patients and examined for KiSS-1 expression by RNase protection assay and in situ hybridization. Patients were divided into arbitrary groups of either high or low KiSS-1 expression and these two categories were correlated with the major clinicopathologic factors in gastric cancer. The presence of venous invasion, tumor recurrence and distant metastasis were statistically correlated with low KiSS-1 expression.
Very strikingly, both overall and disease-free survival were much lower in patients with low KiSS-1 expression. KiSS-1 clearly emerged as the strongest independent prognostic variable.
Although the mechanism of how KiSS-1 is downregulated in gastric cancer and how it directly inhibits venous invasion and metastasis remains to be revealed, this important finding could be extremely useful to monitor the prognosis of gastric cancer.
Integrin-Linked Kinase and Breast Cancer
Various genetic alterations have been implicated in the pathogenesis of human breast cancer. In this study (pages 881–891), Chen and colleagues investigated whether the integrin-linked kinase (ILK), a kinase involved in a number of integrin and growth factor pathways that maps to chromosome 11p, has an influence on tumor growth and metastatic potential in breast cancer.
ILK was mapped precisely to the loss of heterozygosity region on chromosome 11p15.5. Downregulation or complete absence of ILK was observed at both an RNA and protein level in invasive breast tumor tissue from 7 patients compared to normal controls. The highly metastatic human breast carcinoma cell line, MDA-MB-435, that has undetectable levels of ILK was transfected with ILK cDNA and several stable clones were established. Clone TR5 that expressed equivalent amounts of ILK to normal mammary epithelial cell lines had a growth rate decrease of 40% compared to vector control (VC) cells. This effect was attributable to functional ILK because 2 ILK mutants could not inhibit cell growth. Interestingly, ILK expression had no effect on apoptosis but ILK expressing MDA-MB-435 cells had reduced invasiveness in vitro.
These growth-inhibiting effects were also mirrored in vivo. Both TR5 and VC cells were injected into mammary fat pads of nude mice. All mice that received VC developed tumors (n=12) whereas only 16% of mice that received the TR5 ILK transfected cells did. Very low metastasis was seen in mice injected with TR5 cells compared to those administered with VC cells.
The authors concede that these results are in disagreement with studies showing that overexpression of ILK in normal epithelial cells actually resulted in tumorigenicity in nude mice. However, certainly in the context of human breast cancer cell lines, ILK appears to have a very important inhibitory role in cancer growth and its metastasis.
Synthetic Ligand for ErbB2
ErbB2 is a proto-oncogene that is overexpressed in about 30% of breast cancer patients and is associated with a poor prognosis. It is a member of the large ErbB receptor tyrosine kinase family and, to date, no ligand has been identified.
On pages 951–960, Pero et al report on a study in which they have identified peptides that can bind to the extracellular domain of ErbB2. Using a phage display system, they characterize several clones and one, EC-1, bound specifically to the human breast cancer cell line SKBR3 (which overexpresses ErbB2) and to human breast tumor specimens that have demonstrable ErbB2 overexpression. A synthetic peptide based on the sequence of the clone EC-1 could almost completely inhibit binding of the EC-1 clone to the extracellular domain of ErbB2. To assess the functional effect of this peptide, SKBR3 cells were treated with various concentrations of it. EC-1 peptide could inhibit ErbB2 phosphorylation of tyrosine residues Y1248 and Y877, in a dose-dependent fashion. Interestingly, ErbB2 phosphorylation is known to have downstream effects that lead to increased cell proliferation. This finding is also strengthened by the observation that EC-1 peptide could inhibit the proliferation of ErbB2 overexpressing MCF-7 cells but not ErbB2 low expressing cells.
These results demonstrate that small peptides can be synthetically generated to bind receptors that have no known natural ligands and can have potential therapeutic applications.