Genomic structure of the human KDR/flk-1 gene

Molecular profiling, including TERT promoter mutations, of acral lentiginous melanomas

Acral lentiginous melanoma (ALM) is the less common subtype with singular characterization. TERT (human telomerase reverse transcriptase) promoter mutations have being described as recurrent in melanomas and infrequent in ALM, but their real incidence and clinical relevance is unclear. The objectives of this study were to describe the prevalence of TERT promoter mutations in ALM, and correlate with the molecular profile of other drive genes and clinical features. Sixty-one samples from 48 patients with ALM were analyzed. After DNA isolation, the mutation profiles of the hotspot region of BRAF, NRAS, KIT, PDGFRA, and TERT genes were determined by PCR amplification followed by direct Sanger sequencing. KIT, PDGFRA, and VEGFR2 gene amplification was performed by quantitative PCR. Clinical information such as survival, clinical stage, and Breslow tumor classification were obtained from medical records. TERT promoter mutations were found in 9.3% of the cases, BRAF in 10.3%, NRAS in 7.5%, KIT in 20.7%, and PDGFRA in 14.8% of ALM. None of the cases showed KIT, PDGFRA, or VEGFR2 gene amplification. We found an association between KIT mutations and advanced Clark level (IV and V, P=0.043) and TERT promoter mutations with low mitotic index. No other significant associations were observed between mutation profile and patients' clinical features nor survival rates. Oncogenic TERT promoter mutations are present in a fraction of ALMs. No relevant associations were found between TERT mutation status and clinical/molecular features nor survival. Mutations of KIT and PDGFRA are the most common genetic alterations, and they can be therapeutic targets for these patients.

Two isoforms of Flk-1 transcripts in early diabetic rat retinas

BACKGROUND

We studied the expression levels of genes encoding the two isoforms of fetal liver kinase-1 (Flk-1) and the effect of intravitreal injection of triamcinolone acetonide (IVTA) in diabetic rat retinas on the isoforms.

METHODS

The right eyes of both streptozotocin-induced diabetic and non-diabetic rats received triamcinolone treatment, while the left eyes were sham-treated, thereby providing four treatment groups. Three pairs of polymerase chain reaction (PCR) primers were designed to specifically amplify the total, long and truncated isoforms of rat Flk-1 mRNA. Gene transcriptional levels of the two isoforms were evaluated using quantitative PCR reaction (real time RT-PCR). To detect the gene activities, standard efficiency standard curves were set up for each of the candidate isoforms.

RESULTS

The transcripts level of the long form Flk-1 is about 4.3 times higher than the level of the short form in the sham-treated normal rat retinas. The expression of the total, long and short form of Flk-1 was up-regulated by 1.5, 1.8 and 0.7 fold, respectively in sham-treated diabetic retinas compared with the sham-treated non-diabetic retinas. IVTA inhibited the expression of the total, long and short forms of Flk-1 by 1.2, 2.0 and 0.3 fold, respectively in the IVTA-treated diabetic compared with sham-treated retinas. There was no statistically significant difference in the expression of the total and short form of Flk-1 in IVTA-treated diabetic/non-diabetic retinas compared with the sham-treated diabetic/non diabetic retinas.

CONCLUSION

The long form of Flk-1 is the predominant mediator of VEGF-A in the pathogenesis of diabetic retinopathy (DR) and can be significantly inhibited by the IVTA treatment. The short form, which cannot be phosphorylated, does not appear to contribute to the pathogenesis of DR. Further research is warranted to establish whether the truncated form of Flk-1 can be used clinically as a dominant negative inhibitor of the effects of Vascular Endothelial Growth Factor (VEGF).

Screening of the transcriptional regulatory regions of vascular endothelial growth factor receptor 2 (VEGFR2) in amyotrophic lateral sclerosis

BACKGROUND

Vascular endothelial growth factor (VEGF) has neurotrophic activity which is mediated by its main agonist receptor, VEGFR2. Dysregulation of VEGF causes motor neurone degeneration in a mouse model of amyotrophic lateral sclerosis (ALS), and expression of VEGFR2 is reduced in motor neurones and spinal cord of patients with ALS.

METHODS

We have screened the promoter region and 4 exonic regions of functional significance of the VEGFR2 gene in a UK population of patients with ALS, for mutations and polymorphisms that may affect expression or function of this VEGF receptor.

RESULTS

No mutations were identified in the VEGFR2 gene. We found no association between polymorphisms in the regulatory regions of the VEGFR2 gene and ALS.

CONCLUSION

Mechanisms other than genetic variation may downregulate expression or function of the VEGFR2 receptor in patients with ALS.

Expression of a flt-4 (VEGFR3) splicing variant in primary human prostate tumors. VEGF D and flt-4t(Delta773-1081) overexpression is diagnostic for sentinel lymph node metastasis

Utilizing a cDNA expression library established from human prostate PC-3ML tumor cells, we have cloned a truncated flt-4 gene, termed flt-4t(Delta773-1081). We have then utilized RNase protection and ELISA to measure the relative levels of VEGF B, C, D and flt-1, KDR, flt-4 and flt-4t(Delta773-1081) expression in freshly isolated benign prostatic hyperplasia or BPH tissue (n=21), primary prostate cancers (n=82) and matching sentinel lymph node metastases from stage T2a-T2b/T3 tumors (n=52). Comparisons of the primary tumors with BPH showed that there was a significant upregulation of VEGF-B (P=0.003), VEGF D (P=0.005), flt-1 (P=0.003), KDR (P=0.002), flt-4 (P=0.007), and flt-4t(Delta773-1081) (P=0.001), but not VEGF-C (P=0.543). There was no correlation between VEGF-B and its receptor flt-1 (P=0.545), or VEGF-C and flt-4 (P=0.16) and KDR (P=0.23) receptor expression in tumor specimens. Conversely, there was no significant relationship between VEGF-D and the flt-4t(Delta773-1081) receptor (P=0.516) expression. Statistical analysis further showed that there was no significant correlation between VEGF-B, VEGF-C, VEGF-D, flt-1, KDR, flt-4 and flt-4t(Delta773-1081) with patient age (P>0.10), stage (P>0.10), PSA value (P>0.15) or tumor size (P>0.15). Likewise, there was no significant correlation between VEGF-B, VEGF-C, flt-1, KDR, and flt-4 with Gleason score (P>0.15). In comparison, flt-4t(Delta773-1081) levels clearly increased significantly in Gleason score 7 and Gleason score 8-10 tumors as well as in stage T2a-T2b/T3 tumors. The studies were extended to compare gene expression profiles in T2a-T2b and T3 tumors with (n=26) and without (n=26) matching sentinel lymph node metastases. The data showed that VEGF D and flt-4t(Delta773-1081) expression levels were significantly elevated in primary tumors with sentinel lymph node involvement compared to those lacking lymph node involvement (P>0.0022 and 0.006, respectively). These data suggest that targeting VEGF D and flt-4t(Delta773-1081) receptors may be particularly effective in the prevention of lymph node metastases.

VEGFR3 gene structure, regulatory region, and sequence polymorphisms

Vascular endothelial growth factor receptor 3 (VEGFR-3) is required for cardiovascular development during embryogenesis. In adults, this receptor is expressed in lymphatic endothelial cells, and mutant VEGFR3 alleles have been implicated in human hereditary lymphedema. To better understand the basis of its specific endothelial lineage-restricted expression, we have characterized the VEGFR3 gene and its regulatory 5' flanking region. The human gene contains 31 exons, of which exons 30a and 30b are alternatively spliced. The VEGFR3 proximal promoter is TATA-less and contains stretches of sequences homologous with the mouse Vegfr3 promoter region. In transfection experiments of cultured cells, the Vegfr3 promoter was shown to control endothelial cell-specific transcription of downstream reporter genes. This result was further confirmed in vivo; in a subset of transgenic mouse embryos, a 1.6 kb Vegfr3 promoter fragment directed weak lymphatic endothelial expression of the LacZ marker gene. This suggests that endothelial cell-specific elements occur in the proximal promoter, although further enhancer elements are probably located elsewhere. The sequence, organization, and variation in the VEGFR3 gene and its regulatory region provide important tools for the molecular genetic analysis of the lymphatic system and its disorders.

Increasing endothelial cell specific expression by the use of heterologous hypoxic and cytokine-inducible enhancers

One of the current challenges in gene therapy is to construct a vector that will target specific tissues. Targeting expression to endothelium is of particular interest in the treatment of several pathologies. We have shown previously that defined regions of the E-selectin and KDR promoters confer endothelial cell specific expression following retroviral delivery. However, the levels of expression were low. In an attempt to increase expression but to preserve the tissue specificity we have examined hypoxic and cytokine-inducible enhancer elements in combination with the KDR and E-selectin promoters. Both enhancers should be active in the tumour environment, boosting expression and giving additional specificity of gene expression in the tumour endothelium. The hypoxia response element (HRE) of the murine phosphoglycerate kinase-1 (PGK-1) promoter was used as a hypoxic enhancer and the tandem-binding site for NFKB from the murine vascular cell adhesion molecule-1 (VCAM-1) promoter as a cytokine-inducible enhancer. The HRE conferred hypoxia inducibility to the KDR and E-selectin promoters. Endothelial specificity of expression was retained with the KDR but not the E-selectin promoter. The NFKB-binding site conferred responsiveness to TNF-alpha to the KDR promoter, however the level of induction was less than that achieved with the HRE. Retrovirus combining both enhancer elements transferred inducibility by hypoxia and TNF-alpha, and reached the highest expression levels upon stimulation. These results confirm that heterologous enhancer elements may operate on a single endothelial cell specific promoter. These findings make the use of inducible enhancers a promising strategy for increasing tissue specific gene expression.

The human herpesvirus 8 homolog of Epstein-Barr virus SM protein (KS-SM) is a posttranscriptional activator of gene expression

Homologs of the Epstein-Barr virus (EBV) SM protein exist in several human and nonhuman herpesviruses. Structure and function differ significantly among these proteins. We have cloned and characterized the human herpesvirus 8 (HHV8) gene, KS-SM, which is homologous to the EBV SM and herpes simplex virus ICP27 genes, from an HHV8-infected primary effusion lymphoma. KS-SM is shown to be a posttranscriptional activator of gene expression in cotransfection studies. KS-SM activated gene expression in a gene-specific, promoter-independent manner. In particular, KS-SM enhanced the expression of KDR/flk-1, a receptor for vascular endothelial growth factor (VEGF), in cotransfection studies. Since expression of KDR/flk-1 is increased in Kaposi's sarcoma and HHV8-infected cell cultures and VEGF enhances the proliferation of HHV8-infected cells, KS-SM may play a pathogenic role in Kaposi's sarcoma.

The human KDR/flk-1 gene contains a functional initiator element that is bound and transactivated by TFII-I

KDR/flk-1, the receptor for vascular endothelial growth factor, is required for normal vascular development. KDR/flk-1 is a TATA-less gene, containing four upstream Sp1 sites and a single transcription start site, although analysis of the start site sequence discloses only weak similarities with the consensus initiator element (Inr) sequence. In vitro transcription assays, however, demonstrate that the region from -10 to +10 relative to the start site contains Inr activity that is orientation- and position-dependent, and mutagenesis of the KDR/flk-1 Inr reduces promoter activity to 28% of the wild-type promoter in transient transfection assays. Gel shift assays confirm that nuclear proteins specifically bind the Inr, and competition experiments demonstrate that TFII-I, a multifunctional Inr-binding nuclear protein, is a component of these DNA-protein complexes. TFII-I transactivates the wild-type KDR/flk-1 promoter, but not a promoter containing a mutated Inr, in transient transfection assays. Immunodepletion of TFII-I from nuclear extracts prior to in vitro transcription assays abolishes transcription from the KDR/flk-1 Inr, an effect that can be rescued by adding back purified TFII-I, reflecting the importance of TFII-I in KDR/flk-1 Inr activity. These experiments demonstrate that the KDR/flk-1 gene contains a functional Inr that is bound by TFII-I and that both the functional Inr and TFII-I activity are essential for transcription.