Inhibition of apoptosis by normal and aberrant Fli-1 and erg proteins involved in human solid tumors and leukemias

Two ets family members, namely erg and Fli-1 are fused with two EWS family members namely EWS and TLS/FUS as a result of chromosome translocation in human solid tumors and leukemias. EWS-erg and EWS-Fli-1, which are involved in greater than 95% of Ewing family of tumors, were shown to function as transcriptional activators. TLS/FUS-erg, which is involved in human myeloid leukemias also functions as a transcriptional activator. Expression of these fusion proteins (EWS-erg and EWS-Fli-1) are shown to be essential for maintaining the oncogenic and tumorigenic properties of tumor cells. Cancer is thought to be caused not only by uncontrolled cell proliferation but also by deregulation of programmed cell death. Therefore, we have studied the role of normal (Fli-1 and erg) and aberrant fusion proteins (EWS-erg, EWS-Fli-1 and TLS/FUS-erg) in apoptosis. We have found that expression of normal (Fli-1 and erg) and aberrant fusion proteins inhibit the apoptosis of NIH3T3 cells induced by either serum deprivation or by treatment with calcium ionophore. We have also observed similar suppression of apoptosis in Ewing's sarcoma cells expressing EWS-Fli-1 and EWS-erg proteins suggesting that these fusion proteins may be responsible for the decreased ability of these tumor cells to undergo apoptosis. Inhibition of the expression of these aberrant fusion proteins by antisense RNA technique resulted in increased susceptibility to apoptosis leading to the death of tumor cells. Therefore, our results suggest that one can use therapeutic agents which can down regulate the expression of fusion proteins in combination with chemotherapeutic agents as an effective treatment for these human solid tumors and leukemias.

Telomerase activity in gynecologic tumors

The standard telomeric repeat assay protocol (TRAP) was used to examine telomerase activity in 16 ovarian tumors, 16 cervical carcinomas, 4 uterine tumors, and 3 vaginal tumors. Telomerase activity was detected in 95% of these tumors, 88% of ovarian malignancies, and 100% of cervical, endometrial, and vaginal malignancies. In contrast, telomerase activity was not evident in normal tissues or in benign proliferative lesions, such as leiomyomas, condyloma acuminata, and simple endometrial hyperplasia. These results suggest that telomerase activation is associated with immortalization or malignant transformation of gynecologic tumors.

Cytologic changes in two cervical carcinoma cell lines after transfection of the wild-type p53 gene

BACKGROUND

To examine morphological changes in cervical carcinoma cells after induction of overexpression of wild-type (wt) p53.

METHOD

A dexamethazone-inducible wt-p53 cDNA was introduced into two cervical carcinoma cell lines (TMCC-1 and ME180) and morphological changes were examined under a phase contrast microscope and following Papanicolaou staining.

RESULTS

TMCC-1 clones obtained by transfection with wt-p53 gene had an altered morphology especially after induction of p53 expression by treatment with dexamethazone. These changes were characterized by cell flattening, multinucleation, micronucleation, and huge giant cells, yet the parental TMCC-1 had none of these morphological changes even after treatment with dexamethazone. Similar cellular changes were observed in ME180 clones obtained by transfection of wt-p53 gene.

CONCLUSION

On the basis of our observations, we propose that the growth inhibition induced by expression of wt-p53 in these cervical carcinoma cell lines carrying HPV DNA sequences is not the result of G1 arrest but rather relates to a blockade in the M phase of the cell cycle.

Reconstruction of the mitral annulus with porcine pericardium--report of a case with mitral annular disruption due to staphylococcal endocarditis

A 60-year-old man was admitted to our hospital for investigation of dyspnea and disorientation with right hemiplegia. Echocardiography showed thickened mitral valve leaflets with vegetations and severe mitral regurgitation. Blood cultures grew Staphylococcus aureus. During the operation, perforation and destruction of the mitral valve leaflets and vegetations were confirmed. Debridement of the infected tissues resulted in segmental disruption of the posterior mitral fibrous annulus. Reconstruction of the mitral annulus with porcine pericardium treated with glutaraldehyde and mitral valve replacement were successful. The patient's postoperative course was complicated with metastatic cerebral and splenic abscesses. After splenectomy on the 8th postoperative day, he gradually recovered without major neurologic sequelae. We believe that reconstruction of the mitral valve annulus with pericardium, especially autologous pericardium, is reliable and useful for the treatment of patients with disruption of the mitral valve annulus.

Growth suppression of a cervical cancer cell line (TMCC-1) by the human wild-type p53 gene

To investigate the effects of human wild-type p53 expression on the proliferation of cervical carcinoma cells, a plasmid, pMO7-hp53, which contains a full-length cDNA of the human wild-type p53 (wt-p53) gene, was transfected into a cell line (TMCC-1) derived from an endocervical type, human papilloma virus-positive adenocarcinoma of the uterine cervix. The exogenous wt-p53 expression induced growth suppression, morphological changes, and loss of anchorage-independent growth of the tumor cells. As the wt-p53 gene apparently plays a negative role in growth regulation of cervical carcinoma cells, this gene may possibly be of some use for treating subjects with a cervical carcinoma.

Loss of tumorigenicity of Ewing's sarcoma cells expressing antisense RNA to EWS-fusion transcripts

Cytogenetic analysis of Ewing's sarcoma, primitive neuroectodermal tumors and Askin tumors revealed characteristic translocations t(11;22) or t(21;22). Molecular analysis of these translocations revealed 5'-region of EWS gene (from band 22q12) is fused to the 3'-region of either Fli-1 gene (from band 11q24) or erg gene (from band 21q22). Functional characterization of the EWS-Fli-1 and EWS-erg chimeric proteins suggested that they function as transcriptional activators. In order to develop therapeutic agents, it is essential to know whether expression of the EWS-fusion gene products is coupled to tumorigenicity of Ewing's sarcoma cells and if targeting the EWS-fusion products results in loss of tumorigenicity of Ewing's sarcoma cells. For this reason, we have made stable Ewing's sarcomas expressing antisense EWS-Fli-1 or EWS-erg expression plasmids. Expression of antisense EWS fusion transcripts resulted in a significant loss of endogenous EWS-Fli-1 and EWS-erg proteins in Ewing's sarcoma cells. These cells expressing antisense EWS fusion transcripts showed loss of anchorage independent growth and tumorigenicity in nude mice unlike the parental Ewing's sarcoma cells. These results demonstrate the necessity of a certain threshold level of expression of EWS-fusion products in the clonogenicity and tumorigenicity of Ewing's sarcoma cells and therefore emphasizes the importance of targeting the EWS-fusion products as a therapy for Ewing family of tumors.

TLS/FUS fusion domain of TLS/FUS-erg chimeric protein resulting from the t(16;21) chromosomal translocation in human myeloid leukemia functions as a transcriptional activation domain

EWS and TLS/FUS genes, which code for RNA binding proteins are involved in a wide variety of human solid tumors. The TLS/FUS gene is involved both in human myxoid liposarcomas which carry a characteristic chromosomal translocation, t(12;16)(q13;p11) and in human myeloid leukemias with recurrent chromosomal translocation, t(16;21)(p11:q22). The TLS/FUS gene is fused to a transcriptional repressor, CHOP (in human myxoid liposarcomas) or transcriptional activator, erg (in human myeloid leukemias). To understand better the functional role of TLS/FUS-erg in human myeloid leukemias, we have cloned the TLS/FUS and TLS/FUS-erg cDNAs and studied the functional properties of their gene products. TLS/FUS protein binds to RNA in vitro and shows preferential binding to poly G. Both the amino- and the carboxy- terminal regions of TLS/FUS containing the conserved RNA binding motifs are needed for poly G specific RNA binding activity. The TLS/FUS fusion domain (TFD) appears to regulate the DNA binding activity of TLS/FUS-erg chimeric protein which shows weaker transcriptional activation properties compared to normal erg proteins. Mutational analysis of the TLS/FUS-erg chimeric protein reveals TFD to function as a transcriptional activation domain thus replacing the amino terminal transcriptional activation domain of the erg protein. Therefore alterations in both DNA binding and transcriptional activation properties of aberrant erg proteins may be responsible for the genesis of t(16;21) chromosomal translocation-bearing human myeloid leukemias.

The EWS gene, involved in Ewing family of tumors, malignant melanoma of soft parts and desmoplastic small round cell tumors, codes for an RNA binding protein with novel regulatory domains

The EWS gene, which maps to band q12 of human chromosome 22, is involved in a wide variety of human solid tumors including Ewing sarcoma, related primitive neuroectodermal tumors, malignant melanoma of soft parts and desmoplastic small round cell tumors. In these tumors, the EWS is fused to genes encoding transcriptional activators/repressors, like Fli-1 or erg or ATF 1 or wt1. To better understand the function of the EWS protein, we cloned the EWS cDNA. Sequence analysis of this cDNA revealed differential splicing involving two exons encoding 72 amino acids. Both alternatively spliced transcripts, EWS and EWS-b, are expressed in a variety of cells. Because EWS proteins contain putative conserved RNA binding motifs, we studied the RNA binding properties of the EWS protein. The EWS-b protein binds to RNA in vitro and, specifically, to poly G and poly U. The RNA binding activity was localized to the carboxy terminal 86 amino acids, which constitute RGG box. Thus the amino terminal domain of EWS (NTD-EWS), which is involved in chromosome translocation may regulate the specificity of RNA binding activity of EWS. An EWS-erg chimeric protein, which is found in Ewing's sarcoma cells, functions as a transcriptional activator. Mutational analysis of EWS-erg chimeric protein revealed that NTD-EWS functions as a regulatory domain for the transcriptional activation properties of EWS-erg chimeric protein.