Expression of the beta 4 integrin subunit induces monocytic differentiation of 32D/v-Abl cells

Dynamic Regulation of Integrin α6β4 During Angiogenesis: Potential Implications for Pathogenic Wound Healing

OBJECTIVE

Angiogenesis is an essential component of normal cutaneous wound repair, but is altered in pathogenic forms of wound healing, such as chronic wounds and fibrosis. We previously reported that endothelial expression of integrin α₆β₄ is developmentally regulated, with α₆β₄ expression correlating with tissue maturation and further showed that endothelial α₆β₄ is downregulated in explant angiogenesis assays. These data support the hypothesis that dynamic regulation of α₆β₄ may play an important role during new vessel formation in healing wounds.

APPROACH

To test this hypothesis, we examined the endothelial expression of α₆β₄ using a murine model of cutaneous wound healing and in vitro cultures of primary human dermal microvascular endothelial cells (HDMECs).

RESULTS

Expression of α₆β₄ is downregulated during early stages of wound healing; angiogenic vessels in day 7 wounds do not express α₆β₄. Endothelial expression of α₆β₄ is resumed in day 14 wounds. Moreover, explanted HDMECs do not express α₆β₄, but expression is induced by treatment with histone deacetylase inhibitors.

INNOVATION

We provide in vivo data supporting a role for the dynamic regulation of α₆β₄ during vessel formation and remodeling during cutaneous wound repair and in vitro findings that suggest endothelial β₄ expression is regulated transcriptionally, providing an important foundation for future studies to understand the transcriptional mechanisms involved in endothelial cell maturation during normal wound repair.

CONCLUSION

Our data indicate that α₆β₄ is dynamically regulated during angiogenesis and vessel maturation and suggest that disruption of this regulation may contribute to defective angiogenesis associated with diabetic wounds or cutaneous fibrosis.

Review of therapeutic options and the management of patients with myelodysplastic syndromes

Myelodysplastic syndromes (MDS) are a poorly understood group of disorders caused by one or more genetic aberrations in the bone marrow-derived cell line responsible for hematopoiesis. Recent advances in genetic medicine have offered new insights into the epigenesis as well as the prognosis of MDS, but have not resulted in new or improved curative treatment options. Bone marrow transplantation, introduced before the advent of genetic medicine, is still the only potential cure. Advances in other medical and pharmaceutical areas have broadened the scope of supportive care and disease-modifying therapies, and treating physicians now have a broad range of disease management options depending on a patient's likely prognosis. There is now clear evidence that appropriate supportive care and therapeutic intervention can improve progression-free and overall survival of MDS patients.

p73 plays a role in erythroid differentiation through GATA1 induction

The TP73 gene gives rise to transactivation domain-p73 isoforms (TAp73) as well as DeltaNp73 variants with a truncated N terminus. Although TAp73alpha and -beta proteins are capable of inducing cell cycle arrest, apoptosis, and differentiation, DeltaNp73 acts in many cell types as a dominant-negative repressor of p53 and TAp73. It has been proposed that p73 is involved in myeloid differentiation, and its altered expression is involved in leukemic degeneration. However, there is little evidence as to which p73 variants (TA or DeltaN) are expressed during differentiation and whether specific p73 isoforms have the capacity to induce, or hinder, this differentiation in leukemia cells. In this study we identify GATA1 as a direct transcriptional target of TAp73alpha. Furthermore, TAp73alpha induces GATA1 activity, and it is required for erythroid differentiation. Additionally, we describe a functional cooperation between TAp73 and DeltaNp73 in the context of erythroid differentiation in human myeloid cells, K562 and UT-7. Moreover, the impaired expression of GATA1 and other erythroid genes in the liver of p73KO embryos, together with the moderated anemia observed in p73KO young mice, suggests a physiological role for TP73 in erythropoiesis.

Neural stem cell differentiation is mediated by integrin beta4 in vitro

Neural stem cells are capable of differentiating into three major neural cell types, but the underlying molecular mechanisms remain unclear. Here, we investigated the mechanism by which integrin beta4 modulates mouse neural stem cell differentiation in vitro. Inhibition of endogenous integrin beta4 by RNA interference inhibited the cell differentiation and the expression of fibroblast growth factor receptor 2 but not fibroblast growth factor receptor 1 or fibroblast growth factor receptor 3. Overexpression of integrin beta4 in neural stem cells promoted neural stem cell differentiation. Furthermore, integrin beta4-induced differentiation of neural stem cells was attenuated by SU5402, the inhibitor of fibroblast growth factor receptors. Finally, we investigated the role of integrin beta4 in neural stem cell survival: knockdown of integrin beta4 did not affect survival or apoptosis of neural stem cells. These data provide evidence that integrin beta4 promotes differentiation of mouse neural stem cells in vitro possibly through fibroblast growth factor receptor 2.

Evolution of decitabine development: accomplishments, ongoing investigations, and future strategies

Decitabine (5-aza-2'-deoxycytidine) is a hypomethylating agent with a dual mechanism of action: reactivation of silenced genes and differentiation at low doses, and cytotoxicity at high doses. The original studies in the 1980s used decitabine as a classical anticancer drug, at its maximum clinically tolerated dose, 1500 to 2500 mg/m(2) per course. At these doses, decitabine was found to be active in leukemia, but was associated with delayed and prolonged myelosuppression. After a better understanding of epigenetics in cancer and the role of decitabine in epigenetic (hypomethylating) therapy was gained, it was reevaluated at approximately 1/20th of the previous doses (ie, at 'optimal biologic' doses that modulate hypomethylation). In these dose schedules of decitabine (100 to 150 mg/m(2) per course), the drug was found to be active with manageable side effects in patients with myelodysplastic syndromes (MDS) and other myeloid tumors. Optimizing dosing schedules of decitabine to maximize hypomethylation (low dose, high dose intensity, and multiple cycles) have further improved results, suggesting that decitabine is an active therapy that alters the natural course of MDS. Combination therapies that augment the epigenetic effect of decitabine will likely improve responses and extend its use for the treatment of other malignancies.

Clinical experience with decitabine in North American patients with myelodysplastic syndrome

Recent evidence demonstrates that epigenetic silencing of genes is associated with myelodysplasia and that a worse prognosis may be correlated with hypermethylation of certain genes, such as the cyclin-dependent kinase inhibitor p15. 5-Aza-2'-deoxycytidine (decitabine, DAC) is a nucleoside analog, which, at low doses, acts as a hypomethylating agent and is fivefold to tenfold more active than 5-azacytidine (azacitidine, Vidaza)--currently the only approved drug for treatment of myelodysplastic syndrome (MDS). Clinical studies have demonstrated that decitabine has activity in patients with MDS. Preliminary results of a phase III multicenter North American trial comparing low-dose decitabine to supportive care verified that therapy with decitabine resulted in higher response rates, improved quality of life, and prolonged time to leukemic transformation and/or death. However, further elucidation of its mechanism of action is required, as clinical response to decitabine does not correlate with demethylation of the p15 gene promoter or the repetitive DNA element LINE. Decitabine appears to upregulate both hypermethylated and nonmethylated genes. Ongoing studies aim to determine the optimal dose, schedule, and route of administration of decitabine, and to evaluate whether efficacy can be improved by using it in combination with other agents, such as histone deacetylase inhibitors.

The myelodysplastic syndromes

The myelodysplastic syndrome(s) (MDS), bone marrow stem cell malignancies that share pathogenetic overlap with acute myeloid leukemia, are characterized by peripheral blood cytopenias and, in more advanced subtypes, varied degrees of maturation arrest. Premature apoptosis of bone marrow cellular elements contributes to ineffective hematopoiesis, which is exacerbated by stromal production of inflammatory cytokines. Abrogation of the effects of these cytokines represents an area of active clinical research, particularly in the treatment of low-risk MDS. In high-risk MDS, the activation of oncogenes and the inactivation of tumor suppressor genes predominate over inhibitory cytokines as proliferation predominates over apoptosis. Agents such as thalidomide, lenalidomide and the hypomethylating drugs 5-azacytidine and decitabine have shown promising efficacy and tolerability in clinical trials, and may represent a springboard for future treatment combinations.

Second complete remission in an elderly patient with acute myeloid leukemia retreated with decitabine

A 67-year-old man with acute myeloid leukemia (AML) was treated with low-dose decitabine. He achieved a complete remission (CR) after two cycles of therapy, and he remained in remission during 1 year of treatment. He developed recurrent AML after discontinuation of decitabine. He was retreated with decitabine and again achieved a CR, which has been maintained for 6 months. This case demonstrates that durable responses can occur upon retreatment with decitabine.

Decitabine improves patient outcomes in myelodysplastic syndromes: results of a phase III randomized study

BACKGROUND

Aberrant DNA methylation, which results in leukemogenesis, is frequent in patients with myelodysplastic syndromes (MDS) and is a potential target for pharmacologic therapy. Decitabine indirectly depletes methylcytosine and causes hypomethylation of target gene promoters.

METHODS

A total of 170 patients with MDS were randomized to receive either decitabine at a dose of 15 mg/m2 given intravenously over 3 hours every 8 hours for 3 days (at a dose of 135 mg/m2 per course) and repeated every 6 weeks, or best supportive care. Response was assessed using the International Working Group criteria and required that response criteria be met for at least 8 weeks.

RESULTS

Patients who were treated with decitabine achieved a significantly higher overall response rate (17%), including 9% complete responses, compared with supportive care (0%) (P < .001). An additional 12 patients who were treated with decitabine (13%) achieved hematologic improvement. Responses were durable (median, 10.3 mos) and were associated with transfusion independence. Patients treated with decitabine had a trend toward a longer median time to acute myelogenous leukemia (AML) progression or death compared with patients who received supportive care alone (all patients, 12.1 mos vs. 7.8 mos [P = 0.16]; those with International Prognostic Scoring System intermediate-2/high-risk disease, 12.0 mos vs. 6.8 mos [P = 0.03]; those with de novo disease, 12.6 mos vs. 9.4 mos [P = 0.04]; and treatment-naive patients, 12.3 mos vs. 7.3 mos [P = 0.08]).

CONCLUSIONS

Decitabine was found to be clinically effective in the treatment of patients with MDS, provided durable responses, and improved time to AML transformation or death. The duration of decitabine therapy may improve these results further.

Long-term follow-up results of the combination of topotecan and cytarabine and other intensive chemotherapy regimens in myelodysplastic syndrome

BACKGROUND

Progressive or higher-risk myelodysplastic syndrome (MDS) is often treated with intensive chemotherapy regimens used for acute myelogenous leukemia (AML). Patients with MDS are often older and may have contraindications to anthracycline-based regimens. Topotecan-cytarabine regimens have shown encouraging results in higher-risk MDS. The aim of this study was to analyze the long-term results with topotecan-cytarabine versus other intensive chemotherapy regimens in higher-risk MDS.

METHODS

Five hundred ten patients with higher-risk MDS treated with intensive chemotherapy were reviewed. Their median age was 63 years; 82% had intermediate 2 or high-risk MDS; 32% had secondary MDS; 40% had chromosome 5 or 7 abnormalities. Therapy was: topotecan-cytarabine in 77; idarubicin-cytarabine regimens in 270; topotecan-cytarabine and cyclophosphamide in 67; fludarabine-cytarabine in 96. Univariate and multivariate analyses were conducted to evaluate the independent associations of different variables, and most important, the treatment regimen, with complete response, induction mortality, and survival.

RESULTS

The overall complete response (CR) rate was 55%, induction mortality 17%, and 5-year survival rate 8%. The 5-year survival rate was 11% for patients younger than 65 years old and 17% for patients with a normal karyotype. Among 82 patients younger than 65 years with a normal karyotype, the CR rate was 67%, 5-year survival rate 27%, and 5-year CR duration rate 33%. Topotecan-cytarabine regimens were equivalent to idarubicin-cytarabine regimens in relation to CR rates and survival rates, but were associated with a lower induction mortality. Multivariate analysis confirmed that treatment regimens were not associated with independent significant differences in CR rates or survival. However, topotecan-cytarabine regimens were still selected to be associated with lower induction mortality rates.

CONCLUSIONS

This analysis suggests that topotecan-cytarabine regimens are equally effective to other AML regimens in higher-risk MDS and may be less toxic. Topotecan-cytarabine may be considered a reasonable alternative to idarubicin-cytarabine in higher-risk MDS, particularly in older patients with contraindications to anthracyclines.

New agents in myelodysplastic syndromes

Myelodysplastic syndromes (MDS) are a heterogeneous group of clonal hematopoietic disorders characterized by ineffective hematopoiesis resulting in peripheral cytopenia and by increased progression to acute myeloid leukemia (AML). Therapeutic interventions for MDS other than allogeneic stem cell transplantation have been palliative. Novel and targeted therapeutic agents such as the inhibition of farnesyltransferases and receptor tyrosine kinases, more potent thalidomide analogs, arsenic trioxide, immunomodulating agents, hypomethylating agents, and histone deacetylase inhibitors have shown encouraging results and may offer durable benefit to patients with MDS. Further development of rational therapies and improvements in the outcome of patients with MDS are likely to emerge from an increased understanding of the pathophysiology of these diseases.

Transfusion independence in patients with myelodysplastic syndromes

Anemia is the most common cytopenia associated with myelodysplastic syndromes (MDS). Current management relies on frequent red blood cell (RBC) transfusions and erythroid growth factors to alleviate symptoms. However, the dependence of patients with MDS on repeated RBC transfusions often results in significant clinical and economic consequences, poorer outcomes, and diminished health-related quality of life. In addition, the intensity and duration of RBC transfusion dependence can influence responses to treatment after disease progression. Erythropoietic growth factors may alleviate the need for RBC transfusions in some patients with MDS, although only a minority of patients experience responses. Emerging treatment strategies to reduce or eliminate the need for RBC transfusions in patients with MDS include immunomodulating drugs, immunosuppressive therapy, and differentiating agents. The immunomodulating drug lenalidomide in patients who have MDS with 5q deletion is unique among emerging approaches, in that cytogenetic remitting activity and durable erythroid responses have been achieved. Newer treatments have the potential to improve the care of patients with MDS by alleviating the clinical, economic, and quality-of-life consequences of long-term RBC transfusion dependence.

deltaEF1 repressor controls selectively p53 family members during differentiation

The discovery of two new p53 homologs, p73 and p63, has defined a family of transcription factors heavily involved in the control of growth suppression, apoptosis, differentiation and development. While p53-deficient mice undergo spontaneous tumors, p73 and p63 knockout mice exhibit severe developmental defects. We demonstrate here that p73 gene is an in vivo transcriptional target of the muscle regulatory factors MyoD, myogenin, Myf5 and Myf6. Ectopic expression of the transcriptional repressor deltaEF1/ZEB/zfhx1a counteracts MyoD/Myf5- or MyoD/Myf6-mediated transcriptional activation of p73. A distinct pattern of in vivo recruitment of muscle regulatory factors and deltaEF1 on p73 regulatory regions was found between proliferating and differentiating muscle cells. We also found that deltaEF1 plays a role in the transcriptional regulation of p53 family members during keratinocytic differentiation. Mouse embryo fibroblasts derived from deltaEF1-deficient mice exhibit unbalanced expression of DeltaNp63, TAp73 and DeltaNp73 but not of TAp63 and p53. The analysis of tissues derived from deltaEF1+/- mice exhibit a selective enrichment of DeltaNp63 in skin.

Drug insight: emerging new drugs in the treatment of myelodysplastic syndromes

Myelodysplastic syndromes (MDS) are a heterogeneous group of hematopoietic stem cell disorders. Although the currently used classification schemes and prognostic algorithms, which are based predominantly on morphologic assessment of blood and marrow smears, have been shown to be valid for defining disease subgroups, they do not take into consideration the significant biological diversity of MDS. As the numerous pathophysiologic pathways that are involved in MDS are being unraveled, new molecular targets are being identified. Novel and targeted therapeutic agents, including inhibitors of farnesyltransferases and receptor tyrosine kinases, more potent thalidomide analogs and epigenetic therapies, have produced encouraging results and might offer durable benefits to patients with MDS. This review intends to provide a concise report on some of the most up-to-date therapies being investigated in MDS.

The silence of the genes: epigenetic disturbances in haematopoietic malignancies

Cancer-associated disturbances of regulated DNA methylation include both global hypomethylation and gene-specific (often even cancer-specific) hypermethylation. Both coexist and have become the subject of intense investigation. In haematological neoplasias, distinct sets of genes, including the p15/INK4b cell cycle inhibitor (mostly in myeloid malignancies) as well as p16/INK4a (only very infrequently in myeloid neoplasia), have been well characterised as to incidence of hypermethylation, concurrent gene inactivation and their re-expression following treatment with DNA methylation inhibitors. Several genes frequently methylated in haematological neoplasias have been studied with respect to their prognostic value. With the advance of low-dose schedules of demethylating agents (explored particularly in the elderly patient population) the rationale for reverting the 'hyper-methylator phenotype' has also prompted in vivo studies of gene reactivation following this type of treatment. However, ubiquitous surrogate markers for the efficacy of this type of treatment need to be developed. These may include reactivated haemoglobin F (HbF), as demethylating agents can result in clinically meaningful induction of HbF in patients with haemoglobinopathies. Because 'cancer testis antigens', which provide powerful signals for T cell cytotoxic activity on solid tumour cells, are usually silenced in leukaemia but can be reactivated in vitro and in vivo, they provide a rationale for an immuno-modulatory effect of demethylating therapy.

Autoimmune disorders in two patients with myelodysplastic syndrome and 5q deletion

Autoimmune diseases occurring concurrently with myelodysplastic syndrome (MDS) with deletion del(5q) including band q31 are very rare and have only been reported twice in the medical literature. We present two additional cases, one patient with del(5q) and trisomy 21 who suffered from rheumatoid arthritis and one patient with isolated del(5q) and autoimmune hemolytic anemia. Both patients had mild leukopenia and severe transfusion-dependent anemia. The rheumatoid arthritis was treated with antirheumatics without additional immunosuppressive medication. Autoimmune hemolytic anemia was controlled with long-term steroid administration. This patient developed additional trisomy 21, 2 years after the initial diagnosis of del(5q). Contrary to previous reports on autoimmune disorders in MDS mentioning improvements of hematological function in response to steroid administration, neither of our patients had a hematological improvement under corticosteroids.

Dormant hypermethylated tumour suppressor genes: questions and answers

The epigenetic inactivation of tumour suppressor genes by promoter CpG island methylation is nowadays one of the hottest topics in cancer research. However, there are still several important open questions: Can we use CpG island hypermethylation to classify tumours according to their clinical behaviour and chemosensitivity? How do we prove that our hypermethylated gene is important for cancer development and/or progression? Which enzymes are directly responsible for the CpG island hypermethylation of tumour suppressor genes? How is the chromatin structure and molecular environment in and around the hypermethylated CpG islands? Can we wake up these dormant hypermethylated tumour suppressor genes in an epigenetic therapy of cancer? Some answers are provided in this review, but other questions remain unsolved, awaiting the eager epigenetic researcher.

Analysis of p73 expression pattern in acute myeloid leukemias: lack of DeltaN-p73 expression is a frequent feature of acute promyelocytic leukemia

p73, the homologue of p53, is a nuclear protein whose ectopic expression, in p53+/+ and p53-/- cells, recapitulates the most well-characterized p53 effects, such as growth arrest, apoptosis and differentiation. Unlike p53, which is mutated in half of human cancers, p73 is rarely mutated. However, altered expression of the p73 gene has been reported in neuroblastoma, lung cancer, prostate cancer and renal cell carcinoma. To investigate the potential involvement of p73 in acute myeloid leukemias (AMLs), we analyzed 71 samples from AML patients for the expression pattern of N-terminal transactivation-p73alpha (TA-p73alpha), its spliced isoforms and N-terminal-deleted-p73 transcripts (DeltaN-p73). We detected p73 gene expression in AML irrespective of FAB (French-American-British) subtypes. Notably, the analysis of DeltaN-p73 expression, which has been reported to inactivate both p53 and p73 antitumor effects, revealed a rather peculiar pattern. In fact, DeltaN-p73 transcript and protein were detectable in 27/28 (96.4%) cases of M0, M1, M2, M4, M5 and M6 AML and in 13/41 (31.7%) cases of PML-RARalpha-positive M3 AML (P<0.01). Thus, the distinct gene expression profile of p73 further supports the notion that acute promyelocytic leukemia is a biologically different subset of AML.

Novel therapies for myelodysplastic syndromes

BACKGROUND

The assessment of patients with myelodysplastic syndromes (MDS) and the choice of therapies remain challenging. New therapies are now emerging after the identification of molecular targets that result in improvement of hematologic parameters and may hold promise for the prevention of disease progression.

METHODS

A review of the English literature was performed that included original articles and related reviews from MEDLINE (PubMed) and abstracts based on published meeting material.

RESULTS

MDS is a heterogeneous group of disorders. Although current classification and prognostic schemes have proven valid to define subgroups, they are insufficient to take into consideration the significant biologic diversity of MDS. New molecular targets are identified as the mosaic of pathophysiologic pathways in MDS is being unraveled. Novel and targeted therapeutic agents, such as the inhibition of farnesyl transferases and receptor tyrosine kinases, more potent thalidomide analogs, and arsenic trioxide, have shown encouraging results and may offer durable benefit to patients with MDS.

CONCLUSIONS

Although progress has been made in the understanding of clinical manifestations and some of the molecular pathways underlying ineffective hematopoiesis and leukemic transformation in MDS, intensive clinical and laboratory research continues to 1) identify further relevant pathophysiologic pathways, 2) better define MDS subgroups, and 3) develop new drugs based on a clearer understanding of disease biology.

The myelodysplastic syndromes: a matter of life or death

Apoptosis is upregulated in early myelodysplastic syndromes (MDS) and may contribute to the peripheral cytopenias commonly observed. Conversely, leukemic progression is associated with abrogation of programmed cell death (PCD). The stage of hematopoietic cell maturation at which defects in PCD arise and the underlying causes of apoptosis dysregulation remain unknown. This paper outlines the apoptotic process in normal hematopoietic cells and summarizes current data regarding the role, potential causes and clinical implications of altered apoptosis in MDS.

Results of decitabine (5-aza-2'deoxycytidine) therapy in 130 patients with chronic myelogenous leukemia

BACKGROUND

General and site-specific DNA methylation is associated with tumor progression and resistance in several cancers, including chronic myelogenous leukemia (CML). Decitabine is a hypomethylating agent that has shown encouraging preliminary anti-CML activity. This study evaluated the activity and toxicity of decitabine in different phases of CML.

METHODS

One hundred and thirty patients with CML were treated: 123 with Philadelphia chromosome (Ph)-positive CML (64 blastic, 51 accelerated, 8 chronic) and 7 with Ph-negative CML. Decitabine was given at 100 mg/m(2) over 6 hours every 12 hours x 5 days (1000 mg/m(2) per course) in the first 13 patients, 75 mg/m(2) in the subsequent 33 patients, and 50 mg/m(2) in the remaining 84 patients.

RESULTS

A total of 552 courses were given to the 130 patients. Only four patients (3%) died during the first course from myelosuppressive complications (three patients) or progressive disease (one patient). Of 64 patients in the CML blastic phase, 18 patients (28%) achieved objective responses. Of these 18 patients, 6 achieved complete hematologic responses (CHR), 2 achieved partial hematologic responses (PHR), 7 achieved hematologic improvements (HI), and 3 returned to the second chronic phase (second CP). Five patients (8%) had cytogenetic responses. Among 51 patients in the accelerated phase, 28 patients (55%) achieved objective responses (12 CHR, 10 PHR, 3 HI, and 3 second CP). Seven patients (14%) had cytogenetic responses. Among eight patients treated in the chronic phase, five (63%) had objective responses. Of seven patients treated for Ph-negative CML, four (57%) had objective responses. There was no evidence of a dose-response effect. The estimated 3-year survival rate was less than 5% in the blastic phase and 27% in the accelerated phase. The only significant toxicity reported was severe myelosuppression, which was delayed, prolonged, and dose dependent. With decitabine 50-75 mg/m(2), the median time to granulocyte recovery above 0.5 x 10(9)/L was about 4 weeks. Myelosuppression-associated complications included febrile episodes in 37% and documented infections in 34%.

CONCLUSIONS

Decitabine appears to have significant anti-CML activity. Future studies should evaluate lower-dose, longer-exposure decitabine schedules alone in imatinib-resistant CML, as well as combinations of decitabine and imatinib in different CML phases.

Identification of direct p73 target genes combining DNA microarray and chromatin immunoprecipitation analyses

The newly discovered p53 family member, p73, has a striking homology to p53 in both sequence and modular structure. Ectopic expression of p73 promotes transcription of p53 target genes and recapitulates the most characterized p53 biological effects such as growth arrest, apoptosis, and differentiation. Unlike p53-deficient mice that develop normally but are subject to spontaneous tumor formation, p73-deficient mice exhibit severe defects in the development of central nervous system and suffer from inflammation but are not prone to tumor development. These phenotypes suggest different biological activities mediated by p53 and p73 that might reflect activation of specific sets of target genes. Here, we have analyzed the gene expression profile of H1299 cells after p73alpha or p53 activation using oligonucleotide microarrays capable of detecting approximately 11,000 mRNA species. Our results indicate that p73alpha and p53 activate both common and distinct groups of genes. We found 141 and 320 genes whose expression is modulated by p73alpha and p53, respectively. p73alpha up-regulates 85 genes, whereas p53 induces 153 genes, of which 27 are in common with p73alpha. Functional classification of these genes reveals that they are involved in many aspects of cell function ranging from cell cycle and apoptosis to DNA repair. Furthermore, we report that some of the up-regulated genes are directly activated by p73alpha or p53.