The expression and cellular localization of phosphorylated VEGFR2 in lymphoma and non-neoplastic lymphadenopathy: an immunohistochemical study

Comparison of vascular endothelial growth factor/vascular endothelial growth factor receptor 2 expression and its relationship to tumor cell proliferation in canine epithelial and mesenchymal tumors

The vascular endothelial growth factor (VEGF)/VEGF receptor 2 (VEGFR2) signaling pathway plays an important role in tumor angiogenesis. VEGFR2 is expressed not only in vascular endothelial cells but also in tumor cells; however, the relationship of VEGF/VEGFR2 expression and tumor proliferation has yet to be elucidated. In addition, since several studies have reported that VEGFR2 inhibitors are more effective against epithelial tumors than mesenchymal tumors, there may be a difference in VEGF/VEGFR2 expression between epithelial and mesenchymal tumors. The purpose of this study was to elucidate differences in VEGF/VEGFR2 expression between epithelial and mesenchymal tumors and the relationship of VEGF/VEGFR2 expression and proliferation in canine tumor cells. We assessed 29 epithelial and 21 mesenchymal canine tumors for microvessel density (MVD), mRNA transcription levels of von Willebrand Factor (vWF) and endoglin, expression of VEGF, VEGFR2, and phosphorylated VEGFR2 (pVEGFR2), and proliferation index (PI) using real-time reverse transcription polymerase chain reaction and immunohistochemistry. VEGFR2 expression on vascular endothelial cells, MVD, and mRNA transcription levels of vWF and endoglin were not significantly different between the two groups. However, expression of VEGF, VEGFR2, and pVEGFR2 was higher in epithelial tumors (P<0.01). Moreover, PI correlated with pVEGFR2 expression in only epithelial tumors (P<0.01, Rs=0.543). These results suggest that the activity of VEGF/VEGFR2 signaling in tumor cells is raised in epithelial tumors, and that this signaling pathway may be related to tumor cell proliferation in epithelial tumors.

The tyrosine kinase receptor ROR1 is constitutively phosphorylated in chronic lymphocytic leukemia (CLL) cells

Phosphorylation of receptor tyrosine kinases (RTKs) has a key role in cellular functions contributing to the malignant phenotype of tumor cells. We and others have previously demonstrated that RTK ROR1 is overexpressed in chronic lymphocytic leukemia (CLL). Silencing siRNA downregulated ROR1 and induced apoptosis of CLL cells. In the present study we analysed ROR1 isoforms and the phosphorylation pattern in CLL cells (n=38) applying western blot and flow-cytometry using anti-ROR1 antibodies and an anti-phospho-ROR1 antibody against the TK domain. Two major ROR1 bands with the size of 105 and 130 kDa respectively were identified, presumably representing unglycosylated (immature) and glycosylated (mature) ROR1 respectively as well as a 260 kDa band which may represent dimerized ROR1. A ROR1 band of 64 kDa that may correspond to a C-terminal fragment was also noted, present only in the nucleus. The 105 kDa ROR1 isoform was more frequently expressed in non-progressive as compared to progressive CLL patients (p=0.03). The 64, 105, 130 and 260 kDa bands were constitutively phosphorylated both at tyrosine and serine residues. Phosphorylation intensity of the mature (130 kDa) isoform was significantly higher in progressive than in non-progressive disease (p<0.001). Incubation of CLL cells with a mouse anti-ROR1 KNG or an anti-ROR1 CRD mAb respectively induced dephosphorylation of ROR1 before entering apoptosis. In conclusion CLL cells expressed different isoforms of ROR1 which were constitutively phosphorylated. The mature, phosphorylated ROR1 isoform was associated with a progressive disease stage. Targeting ROR1 by mAbs induced specific dephosphorylation and leukemic cell death. ROR1 might be an interesting therapeutic target.

Landscape of EGFR signaling network in human cancers: biology and therapeutic response in relation to receptor subcellular locations

The epidermal growth factor receptor (EGFR) pathway is one of the most dysregulated molecular pathways in human cancers. Despite its well-established importance in tumor growth, progression and drug-resistant phenotype over the past several decades, targeted therapy designed to circumvent EGFR has yielded only modest clinical success in cancer patients, except those with non-small cell lung cancer (NSCLC) carrying EGFR activation mutations. However, almost all of these NSCLC patients eventually developed resistance to small molecule EGFR kinase inhibitors. These disappointing outcomes are, in part, due to the high complexity and the interactive nature of the EGFR signaling network. More recent compelling evidence further indicates that EGFR functionality can be dependent on its subcellular location. In this regard, EGFR undergoes translocation into different organelles where it elicits distinctly different functions than its best known activity as a plasma membrane-bound receptor tyrosine kinase. EGFR can be shuttled into the cell nucleus and mitochondrion upon ligand binding, radiation, EGFR-targeted therapy and other stimuli. Nuclear EGFR behaves as transcriptional regulator, tyrosine kinase, and mediator of other physiological processes. The role of mitochondrial EGFR remains poorly understood but it appears to regulate apoptosis and autophagy. While studies using patient tumors have shown nuclear EGFR to be an indicator for poor clinical outcomes in cancer patients, the impact of mitochondrial EGFR on tumor behavior and patient prognosis remains to be defined. Most recently, several lines of evidence suggest that mislocated EGFR may regulate tumor response to therapy and that plasma membrane-bound EGFR elicits survival signals independent of its kinase activity. In light of these recent progresses and discoveries, we will outline in this minireview an emerging line of research that uncovers and functionally characterizes several novel modes of EGFR signaling that take center stage in the cell nucleus, mitochondrion and other subcellular compartments. We will also discuss the clinical implications of these findings in the rationale design for therapeutic strategy that overcomes tumor drug resistance.

Nuclear localization of orphan receptor protein kinase (Ror1) is mediated through the juxtamembrane domain

Background

Several receptor tyrosine kinases (RTKs) such as EGFR, FGFR, TRK, and VEGFR are capable of localizing in the cell nucleus in addition to their usual plasma membrane localization. Recent reports also demonstrate that nuclear-localized RTKs have important cellular functions such as transcriptional activation. On the basis of preliminary bioinformatic analysis, additional RTKs, including receptor tyrosine kinase-like orphan receptor 1 (Ror1) were predicted to have the potential for nuclear subcellular localization. Ror1 is a receptor protein tyrosine kinase that modulates neurite growth in the central nervous system. Because the nuclear localization capability of the Ror1 cytoplasmic domain has not been reported, we examined the cellular expression distribution of this region.

Results

The Ror1 cytoplasmic region was amplified and cloned into reporter constructs with fluorescent tags. Following transfection, the nuclear distribution patterns of transiently expressed fusion proteins were observed. Serial deletion constructs were then used to map the juxtamembrane domain of Ror1 (aa_471-513) for this nuclear translocation activity. Further site-directed mutagenesis suggested that a KxxK-16 aa-KxxK sequence at residues 486-509 is responsible for the nuclear translocation interaction. Subsequent immunofluorescence analysis by cotransfection of Ran and Ror1 implied that the nuclear translocation event of Ror1 might be mediated through the Ran pathway.

Conclusions

We have predicted several RTKs that contain the nuclear localization signals. This is the first report to suggest that the juxtamembrane domain of the Ror1 cytoplasmic region mediates the translocation event. Ran GTPase is also implicated in this event. Our study might be beneficial in future research to understand the Ror1 biological signaling pathway.

Differential expression of decorin, EGFR and cyclin D1 during mammary gland carcinogenesis in TA2 mice with spontaneous breast cancer

Background

The Tientsin Albino 2 (TA2) mouse is an inbred strain originating from the Kunming strain. It has a high incidence of spontaneous breast cancer without the need for external inducers or carcinogens. Until now, the mechanism of carcinogenesis has remained unclear. In this study, we investigate differential gene expression, especially the expression of decorin, EGFR and cyclin D1, during mammary gland epithelial cell carcinogenesis in TA2 mice.

Methods

Gene expression profiles of spontaneous breast cancer and matched normal mammary gland tissues in TA2 mice were ascertained using an Affymetrix Mouse 430 2.0 array. Twelve mammary tissue samples from five month-old female TA2 mice (Group A), as well as 28 samples from mammary (Group B) and cancer tissues (Group C) of spontaneous breast cancer-bearing TA2 mice, were subsequently used to detect the expression of decorin, EGFR and cyclin D1 by real-time PCR and immunohistochemical methods.

Results

Several imprinted genes, oncogenes and tumor suppressor genes were differentially expressed between normal mammary gland tissues and breast cancer tissues of TA2 mice. The imprinted gene decorin and the oncogene EGFR were down-regulated in tumor tissues, while the oncogene cyclin D1 was up-regulated. Immunohistochemistry showed that samples in Group A showed high decorin expression more frequently than those in Group B (P < 0.05). More tissue samples in Group B than Group A were positive for nuclear EGFR, and tissue samples in Group B more frequently showed high nuclear EGFR expression than those in Group A or Group C (P < 0.05). The labeling index for cyclin D1 in Group C was significantly higher than in Group B. Mammary tissues of Group A expressed the highest level of decorin mRNA (P < 0.05), and mammary tissues of Group B expressed the highest level of EGFR mRNA (P < 0.05), while cancer tissues expressed the highest level of cyclin D1 mRNA (P < 0.05).

Conclusions

The expression of decorin, EGFR and cyclin D1 in mammary epithelial cells changes with increasing age. The abnormal expression of them may partly contribute to the genesis of spontaneous breast cancer in TA2 mice.

Vascular endothelial growth factor (VEGF)-C - a potent risk factor in children diagnosed with stadium 4 neuroblastoma

To evaluate the immunohistochemical expression of VEGF-C, CD34 and VEGFR-2 in cancer tissue of children diagnosed with stadium 4 neuroblastoma (NB) and correlate their presence with the survival rate of children diagnosed with that stage of the disease. Eighteen children assigned to stadium 4 composed the study group. Fourteen patients (allocated to stadium 3) formed a control group. VEGF-C, CD34 and VEGFR-2 expressions were evaluated by immunohistochemical assay. Consecutive slides incubated with anti-CD34 and anti-VEGFR-2 antibodies revealed that the two markers were colocalized within endothelial layer of the blood vessels. On the other hand, VEGF-C was expressed exclusively in tumour cells. As demonstrated by Fisher's exact test, the risk of NB treatment failure (progression or relapse) as well as tumour related death, when all the patients were considered, was found to be significant in VEGF-C positive patients. VEGF-C expression in NB constitutes a potent risk factor and may direct future anti-angiogenic treatment strategy. The proximity of VEGF-C and CD34/VEGFR-2 of NB could be the equivalent of a potentially interesting VEGF-C fashion involving a tumour cell invasion into the blood vessels in an early phase of metastases promoting.

Nuclear expression of phosphorylated EGFR is associated with poor prognosis of patients with esophageal squamous cell carcinoma

OBJECTIVES

Although it has been reported that epidermal growth factor receptor (EGFR) is able to translocate from the plasma membrane to the nucleus, the pathophysiological role of this translocation in tumorigenicity is still unclear. In the present study, to elucidate the pathophysiological significance of EGFR translocation, we investigated the expression not only of conventional EGFR but also its phosphorylated form (pEGFR), focusing on its cellular localization in esophageal cancer tissues.

METHODS

Fifty-two specimens of esophageal squamous cell carcinoma (SCC) obtained by surgery were examined immunohistochemically for their EGFR and pEGFR immunostaining patterns. The relationships between clinicopathological parameters and EGFR or pEGFR immunostaining patterns were then analyzed.

RESULTS

In 37 (71.2%) of the 52 esophageal SCCs, EGFR immunoreactivity was clearly localized at the plasma membrane of the cancer cells, whereas pEGFR immunoreactivity was clearly localized in the nucleus in 19 (36.5%) cases. Nuclear expression of pEGFR significantly correlated with TNM stage and lymph node metastasis, and moreover was associated with a poor outcome of esophageal SCC.

CONCLUSIONS

Nuclear translocalization of pEGFR is associated with an increase in the malignant potential of esophageal SCC and may affect prognosis in patients with esophageal SCC.

Expression of Vascular Endothelial Growth Factor and its Receptors in Canine Lymphoma

Vascular endothelial growth factor (VEGF) stimulates endothelial cell proliferation and has a pivotal role in tumour angiogenesis. The expression of VEGF and its receptors VEGFR-1 and VEGFR-2 was examined immunohistochemically in 43 specimens of canine lymphoma and in six normal lymph nodes. Western blotting and reverse transcriptase polymerase chain reaction (RT-PCR) were performed to detect VEGF protein and mRNA, respectively. VEGF protein was expressed by 60% of the tumours with diffuse cytoplasmic labelling of the neoplastic cells. Endothelial cells, macrophages and plasma cells were also immunolabelled. VEGFR-1 was expressed by variable numbers of neoplastic cells in 54% of lymphoma specimens. VEGFR-1 was also expressed by macrophages, plasma cells, reticulum cells, and vascular endothelial cells. Macrophages and lymphocytes in germinal centres of normal lymph nodes were also immunoreactive with anti-VEGF and VEGFR-1. Most tumours did not express VEGFR-2 but in 7% of sections there was focal labelling of neoplastic and endothelial cells, with a cytoplasmic and perinuclear pattern. The observed variability in expression of VEGF and its receptors probably relates to the fact that lymphoma is a heterogeneous lymphoproliferative tumour. Individual differences in VEGF and VEGFR expression must be taken into account when VEGF and VEGFR-targeted approaches for anti-angiogenic therapy are considered in dogs.

The significance of VEGF-C/VEGFR-2 interaction in the neovascularization and prognosis of nephroblastoma (Wilms' tumour)

AIM

To investigate the immunohistochemical expression of vascular endothelial growth factor (VEGF)-C and VEGFR-2 in nephroblastoma tissue and correlate their presence with the survival rate of children diagnosed with stage III Wilms' tumour.

METHODS AND RESULTS

The material included nephroblastoma tissue obtained from 25 children hospitalized in the Department of Paediatric Oncology, Haematology and Transplantology between 1997 and 2003. VEGF-C and VEGFR-2 expression was evaluated by immunohistochemical assay. VEGF-C was expressed in all cells of the blastemal component and in 30% of tumour cells in the stromal part. It was absent from epithelial elements. VEGFR-2 expression was spread over the surface of numerous stromal cells as well as all the epithelial cells forming dysplastic tubules. The blastemal component of Wilms' tumour was VEGFR-2-negative. VEGF-C-immunopositive stromal cells were situated in the closest proximity to VEGF-C-immunonegative but VEGFR-2-immunoreactive tubules. VEGF-C expression was of prognostic value for both clinical progression (P = 0.0005) and tumour-related death (P = 0.0365).

CONCLUSIONS

VEGF-C expression in Wilms' tumour constitutes a potent unfavourable risk factor and may direct future antiangiogenic treatment strategies. The proximity of VEGF-C and VEGFR-2 in the stromal and epithelial components of nephroblastoma could be the neoplastic equivalent of the binary VEGF-C function observed in epithelial and endothelial morphogenesis.

Characterization of a novel tripartite nuclear localization sequence in the EGFR family

Aberrant expression of epidermal growth factor receptor (EGFR) is present in many human tumors. Several reports have shown that EGFR is translocated into the nucleus during liver regeneration and in several types of cells and tissues such as placenta and thyroid. Nuclear EGFR is associated with transcription, DNA synthesis, and DNA repair activity and serves as a prognostic marker in breast carcinoma and oropharyngeal squamous cell cancer. However, the nuclear localization sequence (NLS) of EGFR has not been extensively examined. In this study, we have shown that the juxtamembrane region of EGFR harbors a putative NLS with three clusters of basic amino acids (RRRHIVRKRTLRR (amino acids 645-657)) that mediates the nuclear localization of EGFR. We found that this newly characterized tripartite NLS is conserved among the EGFR family members (EGFR, ErbB2, ErbB3, and ErbB4) and is able to move each to the nucleus. Further, this tripartite NLS could also mediate the nuclear localization of other known cytoplasmic proteins such as pyruvate kinase. We have demonstrated that mutating one of the three basic amino acid clusters (R or K --> A) leads to significant impairment of the nuclear localization of EGFR and that of a green fluorescent protein-pyruvate kinase-NLS reporter protein. Our results show that this tripartite NLS is distinct from the traditional mono- and bipartite NLS and reveal a mechanism that could account for the nuclear localization of membrane receptors.

EGFR signaling pathway in breast cancers: from traditional signal transduction to direct nuclear translocalization

Aberrant epidermal growth factor receptor (EGFR) signaling is a major characteristic of many human malignancies including breast cancer. Since the discovery of EGF in 1960's and its receptor in 1980's, our understanding of the EGF/EGFR pathway has been significantly advanced and consequently, EGFR is considered as a major oncogenic factor and an attractive therapeutic target. The well-established traditional function of EGFR is known to transmit extra-cellular mitogenic signals, such as EGF and transforming growth factor-alpha (TGF-alpha), through activating a number of downstream signaling cascades. These include signaling modules that involve phospholipase C-gamma, Ras, and phosphatidylinositol-3 kinase (PI-3K). In cancer cells, the common outcomes following the activation of the EGFR-mediated downstream pathways are altered gene activities, leading to un-controlled tumor proliferation and apoptosis. Interestingly, emerging evidences suggest the existence of a direct mode of the EGFR pathway that is distinct from the traditional transduction pathway. This new mode of EGFR signaling involves cellular transport of EGFR from the cell-surface to the cell nucleus, association of nuclear EGFR complex with gene promoters, and transcriptional regulation of the target genes. Although the nature and pathological consequences of the nuclear EGFR pathway remain elusive, accumulating evidences suggest its association with increased tumor cell proliferation and poor survival rate in breast cancer patients. While several anti-EGFR agents are being tested in breast cancer patients clinically and others under pre-clinical development, a better understanding of the traditional and the nuclear EGFR pathways will facilitate the identification of patients that are likely to respond to these agents as well as future development of more effective anti-EGFR therapeutic interventions.

Nuclear-cytoplasmic transport of EGFR involves receptor endocytosis, importin beta1 and CRM1

Many receptor tyrosine kinases (RTKs) can be detected in the cell nucleus, such as EGFR, HER-2, HER-3, HER-4, and fibroblast growth factor receptor. EGFR, HER-2 and HER-4 contain transactivational activity and function as transcription co-factors to activate gene promoters. High EGFR in tumor nuclei correlates with increased tumor proliferation and poor survival in cancer patients. However, the mechanism by which cell-surface EGFR translocates into the cell nucleus remains largely unknown. Here, we found that EGFR co-localizes and interacts with importins alpha1/beta1, carriers that are critical for macromolecules nuclear import. EGFR variant mutated at the nuclear localization signal (NLS) is defective in associating with importins and in entering the nuclei indicating that EGFR's NLS is critical for EGFR/importins interaction and EGFR nuclear import. Moreover, disruption of receptor internalization process using chemicals and forced expression of dominant-negative Dynamin II mutant suppressed nuclear entry of EGFR. Additional evidences suggest an involvement of endosomal sorting machinery in EGFR nuclear translocalization. Finally, we found that nuclear export of EGFR may involve CRM1 exportin as we detected EGFR/CRM1 interaction and markedly increased nuclear EGFR following exposure to leptomycin B, a CRM1 inhibitor. Collectively, these data suggest the importance of receptor endocytosis, endosomal sorting machinery, interaction with importins alpha1/beta1, and exportin CRM1 in EGFR nuclear-cytoplasmic trafficking. Together, our work sheds light into the nature and regulation of the nuclear EGFR pathway and provides a plausible mechanism by which cells shuttle cell-surface EGFR and potentially other RTKs through the nuclear pore complex and into the nuclear compartment.

Vascular endothelial growth factor C—a potent risk factor in childhood acute lymphoblastic leukaemia: an immunocytochemical approach

AIMS

To investigate the immunocytochemical expression of vascular endothelial growth factor C (VEGF-C) and its receptors (VEGFR-2 and VEGFR-3) in childhood acute lymphoblastic leukaemia (ALL) blasts and to determine the possible role of this complex in the pathogenesis and prognosis of ALL.

METHODS AND RESULTS

Bone marrow samples were taken from 120 children diagnosed with ALL. An indirect immunocytochemical procedure was performed with the use of monoclonal mouse anti-human antibodies against VEGF-C, VEGFR-2 and VEGFR-3 (diluted 1 : 100). The immunocytochemical expression of VEGF-C was confirmed exclusively in the cytoplasm of ALL lymphoblasts (the mean percentage was 36.4 +/- 7.2). It was absent from the cytoplasm of normal haematopoietic cells in the control group. No VEGFR-2 or VEGFR-3 expression was detected in the children of either the study or control groups. The risk of induction failure or leukaemic relapse was found to be significant in all VEGF-C+ patients (P < 0.0001 and P < 0.02, respectively; Fisher's exact test).

CONCLUSIONS

The absence of VEGF-C in blast cells predicts long-lasting remission in all leukaemic children. Our findings also suggest that leukaemic cell invasion, following VEGF-C-driven lymphangiogenesis, could be related to a mediating role of this peptide produced by blast cells themselves.

Expression and significance of vascular endothelial growth factor receptor 2 in bladder cancer

PURPOSE

Vascular endothelial growth factor has a critical role in maintaining tumor microvasculature and, as such, is an attractive target for anti-angiogenic therapy. Aberrant expression of VEGF receptors, especially VEGFR2, on epithelial tumor cells allows VEGF to stimulate growth and migration of tumor cells in an autocrine and/or paracrine manner. Therefore, we studied the expression of VEGF and VEGFR2 in bladder cancer, and the relationship to disease characteristics.

MATERIALS AND METHODS

Expression of VEGF and VEGFR2 was studied in a cohort of 72 patients with transitional cell cancer of the bladder. Tumor tissues from all patients were analyzed by immunohistochemistry and examined by a pathologist blinded to patient outcome. Patient demographics and disease outcome were correlated with expression of these markers. Bladder cancer cell lines that express VEGFR2 were studied in vitro and in vivo to establish the significance of VEGF/VEGFR2 signaling.

RESULTS

Expression of VEGF and VEGFR2 was observed in 58% and 50% of urothelial tumor cells, respectively. VEGF expression failed to correlate with clinical variables. However, VEGFR2 expression correlated with disease stage (coefficient 0.23, p = 0.05). In addition, VEGFR2 expression increased with tumor invasion into the muscle (p <0.01). Experiments with VEGFR2 positive bladder cancer cell lines in vitro demonstrated increased invasion in response to VEGF. In addition, VEGF inhibition augmented the effect of docetaxel in a murine xenograft model of bladder cancer with a significant inhibition in proliferative index and microvascular density, and induction of apoptosis.

CONCLUSIONS

Increased VEGFR2 expression correlates with several features that predict progression of urothelial cancer, including disease stage and invasive phenotype. VEGF targeted therapy may enhance the efficacy of standard therapy for bladder cancer.

Nuclear EGFR signalling network in cancers: linking EGFR pathway to cell cycle progression, nitric oxide pathway and patient survival

Emerging evidences suggest the existence of a new mode of epidermal growth factor receptor (EGFR) signalling pathway in which activated EGFR undergoes nuclear translocalization and subsequently regulates gene expression and potentially mediates other cellular processes. This signalling route is distinct from the better-characterized, traditional EGFR pathway that involves transduction of mitogenic signals through activation of multiple signalling cascades. Transcriptional activity of nuclear EGFR appears to depend on its C-terminal transactivation domain and its physical and functional interaction with other transcription factors that contain DNA-binding activity. Likely via its ability to upregulate gene expression, nuclear EGFR pathway is associated with major characteristics of more aggressive tumours: increased proliferative potential, nitric oxide synthesis, and accelerated G1/S cell cycle progression. A role of nuclear EGFR in prognostic prediction is further suggested in patients with breast carcinomas and oropharyngeal squamous cell carcinomas. It is noted that significant advances were made towards the knowledge of the nuclear EGFR pathway; however, many aspects of this new pathway remain unresolved and will be discussed in this review. As a number of other receptor tyrosine kinases (RTKs) and cytokine receptors also undergo similar nuclear translocalization, a better understanding of the physiological and malignant nature of the nuclear EGFR pathway will likely shed light into the biology of cancer with nuclear RTKs.

Expression and cellular localization of vascular endothelial growth factor A and its receptors in acute and chronic leukemias: An immunohistochemical study

We aimed to study the expression of phosphorylated vascular endothelial growth factor receptor 2 (pVEGFR-2), a membrane-bound tyrosine kinase receptor to vascular endothelial growth factor, in 76 cases of leukemia and nonneoplastic myeloproliferative disease and in 8 reactive bone marrows. The microvessel density (MVD) and the expression of both pVEGFR-2 and its ligand, VEGFA, were evaluated in these cases. We used archival cases and immunohistochemistry with a monoclonal antibody generated by us to the autophosphorylation sites in the cytoplasmic tail of VEGFR-2 and von Willebrand factor antibody to evaluate MVD. Our results demonstrate increased expression of this phosphorylated receptor in the neoplastic cells in acute myeloid and lymphoblastic leukemias. This correlated with increased MVD and VEGFA expression by the neoplastic cells. Interestingly, there was nuclear relocation of this receptor in these diseases. This raises the possibility that pVEGFR-2 may be involved in the transcriptional regulation of these leukemias. Small molecule inhibitors to this receptor may therefore be a useful adjunct in the therapy for these diseases.