Retinoic acid causes MEK-dependent RAF phosphorylation through RARalpha plus RXR activation in HL-60 cells

Retinoic acid (RA) is known to cause the myeloid differentiation of HL-60 human myeloblastic leukemia cells in a process requiring MEK-dependent ERK2 activation. This RA-induced ERK2 activation appears after approximately 4 h and persists until the cells are differentiated and G0 arrested (Yen et al, 1998). This motivates the question of whether RA also activated RAF as part of a typical RAF/MEK/MAPK cascade. Retinoic acid is shown here to also increase the phosphorylation of RAF, but in an unusual way. Surprisingly, increased RAF phosphorylation is first detectable after 12 to 24 hours by phosphorylation-induced retardation of polyacrylamide gel electrophoretic mobility. The RA-induced increased RAF phosphorylation is still apparent after 72 hours of treatment when most cells are differentiated and G0 arrested. There is a progressive dose-response relationship with 10(-8), 10(-7), and 10(-6) M RA. The RA-induced RAF phosphorylation corresponds to increased in vitro kinase activity. Inhibition of MEK with a PD98059 dose which inhibits ERK2 phosphorylation and subsequent cell differentiation also inhibits RAF phosphorylation. RA-induced MEK-dependent RAF phosphorylation is not due to changes in the amount of cellular MEK. The induced RAF phosphorylation, as well as anteceding ERK2 activation, depends on ligand-induced activation of both an RARalpha receptor and an RXR receptor. This and the slow kinetics of activation suggest a need for prior RA-induced gene expression. In summary, RA induces a MEK-dependent prolonged RAF activation, whose slow onset occurs after ERK2 activation but still well before cell cycle arrest and cell differentiation. The RA-induced increased RAF phosphorylation thus differs from typical mitogenic growth factor signaling, features that may contribute to cell cycle arrest and differentiation instead of division as the cellular outcome.

Polyomavirus small t antigen prevents retinoic acid-induced retinoblastoma protein hypophosphorylation and redirects retinoic acid-induced G0 arrest and differentiation to apoptosis

Polyomavirus small t antigen (ST) impedes late features of retinoic acid (RA)-induced HL-60 myeloid differentiation as well as growth arrest, causing apoptosis instead. HL-60 cells were stably transfected with ST. ST slowed the cell cycle, retarding G2/M in particular. Treated with RA, the ST transfectants continued to proliferate and underwent apoptosis. ST also impeded the normally RA-induced hypophosphorylation of the retinoblastoma tumor suppressor protein consistent with failure of the cells to arrest growth. The RA-treated transfectants expressed CD11b, an early cell surface differentiation marker, but inducible oxidative metabolism, a later and more mature functional differentiation marker, was largely inhibited. Instead, the cells underwent apoptosis. ST affected significant known components of RA signaling that result in G0 growth arrest and differentiation in wild-type HL-60. ST increased the basal amount of activated ERK2, which normally increases when wild-type cells are treated with RA. ST caused increased RARalpha expression, which is normally down regulated in RA-treated wild-type cells. The effects of ST on RA-induced myeloid differentiation did not extend to monocytic differentiation and G0 arrest induced by 1,25-dihydroxy vitamin D3, whose receptor is also a member of the steroid-thyroid hormone superfamily. In this case, ST abolished the usually induced G0 arrest and retarded, but did not block, differentiation without inducing apoptosis, thus uncoupling growth arrest and differentiation. In sum, the data show that ST disrupted the normal RA-induced program of G0 arrest and differentiation, causing the cells to abort differentiation and undergo apoptosis.

Retinoic acid-induced blr1 expression requires RARalpha, RXR, and MAPK activation and uses ERK2 but not JNK/SAPK to accelerate cell differentiation

Upstream signaling requirements of retinoic acid (RA)-induced blr1 expression and downstream signaling consequences of blr1 over-expression in a human myeloid leukemia cell line demonstrate that mitogen-activated protein kinase (MAPK) signaling complexes are involved in both avenues. RA-induced myeloid differentiation and G1/G0 growth arrest of HL-60 cells is known to require the activation of the RARalpha and RXR retinoid receptors, as well as activation of the MAPK, ERK2. Transcriptional activation of the Burkitt's lymphoma receptor 1 (blr1) gene occurs early during RA-induced differentiation of HL-60 cells and requires these same three activating processes. The use of retinoid ligands that activate either the RARalpha or the RXR retinoid receptors revealed that blr1 mRNA induction was detectable only when both RARalpha and RXR were activated. Neither the RARalpha nor RXR selective ligands alone induced expression of blr1, but the combination of the two ligands induced the expression of blr1 to the same extent as RA. The MAPKK (MEK) inhibitor, PD98059, was used to determine whether extracellular signal-regulated kinase (ERK2) activation was necessary for induction of blr1 mRNA. PD98059 inhibited induced blr1 mRNA expression, due to RA or activated RARalpha plus RXR ligands, indicating that ERK2 activation is necessary for blr1 mRNA expression. Previous studies showed that ectopic expression of blr1 also caused increased MAPK activation, in particular ERK2, and subsequently accelerated RA-induced differentiation and G1/G0 growth arrest. Inhibition of ERK2 activation inhibited differentiation of blr1 transfectants, suggesting that the accelerated differentiation reflected blr1-enhanced ERK2 activation. The present data also demonstrate that ectopic expression of blr1 increased JNK/SAPK activity, but JNK/ SAPK activation was not needed for accelerated RA-induced differentiation and growth arrest. The results show that the signals known to be required for HL-60 differentiation, activated RARalpha, RXR, and ERK2, are necessary for blr1 mRNA expression. Downstream consequences of blr1 overexpression include enhanced MAPK signaling.

Application of membrane-based dendrimer/DNA complexes for solid phase transfection in vitro and in vivo

In this study a general description of the use of solid support membranes as the device for DNA delivery mediated by PAMAM dendrimers is presented. In contrast to the other DNA carriers, dendrimer/DNA complexes retain the ability to transfect after drying, which enabled coating or incorporation of complexes into poly(DL-lactide-co-glycolide) or collagen-based bioerodable membranes. These studies provide support for the use of this technology for in vitro and in vivo transfection of skin cells. Expression of luciferase or green fluorescent protein from pCF1-Luc and pEGFP1 plasmids indicated that dendrimer/DNA complexes can mediate transfection after dissociation from the solid support and/or when retained on the surface of the membranes. Modification of the membranes by incorporation of an anionic lipid, phosphatidyl glycerol (PG) at 1-5% concentrations, resulted in more efficient in situ transfection, particularly with dendrimer/DNA complexes formed at the low charge ratios (1-5). We also report data supporting the feasibility of membrane-based dendrimer/DNA complexes, particularly formed at lower than neutralizing conditions, for topical in vivo delivery of DNA to hairless mouse skin.

Opposing effects of androgen and estrogen on pituitary-adrenal function in nonpregnant primates

Maternal administration of androstenedione produces a sustained fall in maternal plasma adrenocorticotropic hormone (ACTH) concentrations in the pregnant nonhuman primate. We hypothesize a negative feedback influence on the maternal hypothalamo-pituitary-adrenal (HPA) axis by androgens in primates. This may reflect an important maternal adaptation during pregnancy in primates preventing premature induction of labor by maternal stress. However, androstenedione is precursor for placental estradiol-17beta synthesis, and infusion of androstenedione into pregnant primates elevates maternal plasma estradiol-17beta to term concentrations. Thus, it could be argued that 1) the effects attributed to androstenedione on the maternal HPA axis are mediated by estrogen rather than by androgen and 2) the negative influence of androgens may be on placental ACTH rather than, or in addition to, pituitary ACTH. To discriminate between androgenic and estrogenic effects of androstenedione on pituitary and/or placental ACTH function in primates we measured plasma ACTH, cortisol, and dehydroepiandrosterone sulfate (DHEAS) concentrations in nonpregnant baboons after treatment with either androstenedione or estradiol-17beta. Nine female baboons were studied between 14 and 22 days postpartum prior to estrous cycling. After 2 days of baseline, a continuous i.v. infusion of androstenedione (1.5 mg/kg per h in 10% intralipid, IL) was started at 0900 h and maintained for 9 days in 3 baboons. A similar protocol was carried out in another 3 baboons that received a continuous i.v. infusion of estradiol-17beta (10 microg/kg per h in 10% IL) instead of androstenedione. Three additional baboons received continuous i.v. IL vehicle alone and served as controls. Arterial blood samples (0.5 ml) for measurement of plasma hormones were taken during baseline and after 1, 3, 5, 7, and 9 days of infusion. Baseline plasma ACTH, DHEAS, and cortisol concentrations were similar among all groups. Plasma ACTH did not change during IL, increased following estradiol-17beta, and fell during androstenedione treatment. Accordingly, plasma cortisol and DHEAS concentrations were also unaltered by IL, and both steroids increased during estradiol-17beta treatment. In contrast, plasma cortisol and DHEAS remained unaltered from baseline during androstenedione treatment, despite the fall in plasma ACTH measured at this time. These data in the nonpregnant baboon 1) are consistent with negative feedback on pituitary ACTH by androgens and 2) demonstrate a positive influence on pituitary-adrenal function by estrogen in primates.

Retinoic acid increases amount of phosphorylated RAF; ectopic expression of cFMS reveals that retinoic acid-induced differentiation is more strongly dependent on ERK2 signaling than induced GO arrest is

Retinoic acid is known to cause the myeloid differentiation and G1/0 cell cycle arrest of HL-60 cells in a process that requires mitogen-activated protein/extracellular signal regulated kinase (MEK)-dependent extracellular signal regulated kinase (ERK)2 activation. It has also been shown that ectopic expression of cFMS, a platelet-derived growth factor (PDGF)-family transmembrane tyrosine kinase receptor, enhances retinoic acid-induced differentiation and G1/0 arrest. The mechanism of how the retinoic acid and cFMS signaling pathways intersect is not known. The present data show that the ectopic expression of cFMS results in the differential loss of sensitivity of retinoic acid-induced differentiation or G1/0 arrest to inhibition of ERK2 activation. PD98059 was used to inhibit MEK and consequently ERK2. In wildtype HL-60 cells, PD98059 blocked retinoic acid-induced differentiation; but in cFMS stable transfectants, PD98059 only attenuated the induced differentiation, with the resulting response resembling that of retinoic acid-treated wild-type HL-60. In wild-type HL-60, PD98059 greatly attenuated the retinoic acid-induced G1/0 arrest allied with retinoblastoma (RB) hypophosphorylation; but in cFMS stable transfectants, PD98059 had no inhibitory effect on RB hypophosphorylation and G1/0 arrest. This differential sensitivity to PD98059 and uncoupling of retinoic acid-induced differentiation and G1/0 arrest in cFMS transfectants is associated with changes in mitogen-activated protein kinase signaling molecules. The cFMS transfectants had more activated ERK2 than did the wild-type cells, which surprisingly was not attributable to enhanced mitogen-activated protein-kinase-kinase-kinase (RAF) phosphorylation. Retinoic acid increased the amount of activated ERK2 and phosphorylated RAF in both cell lines. But PD98059 eliminated detectable ERK2 activation, as well as inhibited RAF phosphorylation, in untreated and retinoic acid-treated wild-type HL-60 and cFMS transfectants, consistent with MEK or ERK feedback-regulation of RAF, in all four cases. Since PD98059 blocks the cFMS-conferred enhancement of the retinoic acid-induced differentiation, but not growth arrest, the data indicate that cFMS-enhanced differentiation acts primarily through MEK and ERK2, but cFMS-enhanced G1/0 arrest allied with RB hypophosphorylation depends on another cFMS signal route, which by itself can effect G1/0 arrest without activated ERK2. Ectopic expression of cFMS and differential sensitivity to ERK2 inhibition thus reveal that retinoic acid-induced HL-60 cell differentiation and G1/0 arrest are differentially dependent on ERK2 and can be uncoupled. A significant unanticipated finding was that retinoic acid caused a MEK-dependent increase in the amount of phosphorylated RAF. This increase may help sustain prolonged ERK2 activation.

Retinoic acid-induced blr1 expression promotes ERK2 activation and cell differentiation in HL-60 cells

Retinoids are known to induce the differentiation and cell cycle arrest of human myeloid leukemia cells in vitro. Differential display was used to identify putative early regulatory genes that are differentially expressed in HL-60 human promyelocytic leukemia cells treated with retinoic acid. One of the cDNAs cloned encodes sequences identifying Burkitt's lymphoma receptor 1 (BLR1), a recently described chemokine receptor. Northern blot analysis demonstrates that blr1 mRNA expression increases within 9 h of retinoic acid treatment, well before functional differentiation or G(1)/G(0) growth arrest at 48 h or onset of morphological changes, suggesting a possible regulatory function. The expression of blr1 mRNA is transient, peaking at 72 h when cells are differentiated. blr1 mRNA also is induced by other differentiation-inducing agents, 1alpha,25-dihydroxyvitamin D(3) and DMSO. Induction of blr1 mRNA by retinoic acid is not blocked by the protein synthesis inhibitor cycloheximide. In HL-60 cells stably transfected with blr1 cDNA, ectopic expression of blr1 causes an increase in ERK2 MAPK activation and promotes retinoic acid-induced G(1)/G(0) growth arrest and cell differentiation. The early expression of blr1 mRNA during differentiation, its ability to increase ERK2 activation, and its enhancement of retinoic acid-induced differentiation suggest that blr1 expression may be involved in retinoic acid-induced HL-60 differentiation.

Increased myometrial contracture frequency at 96-140 days accelerates fetal cardiovascular maturation

Fetal cardiovascular responses to an altered intrauterine environment of increased myometrial contractures induced by oxytocin (OT) pulses to the ewe over the final 50 days of gestation were studied in chronically instrumented sheep. Ewes received saline (Cntl) or long-term OT treatment (LTOT, 600 microU x kg(-1) x min(-1) in 5-min pulses every 20 min) from 96 days gestational age. Fetal baroreflex responses to sodium nitroprusside (SNP) and phenylephrine (PE) were studied at 133 days gestation. OT increased contractures in LTOT ewes. Fetal blood pressure (FBP) was higher, and fetal heart rate (FHR) and slope of daily change in FBP and FHR were lower in LTOT fetuses. Fetal SNP-induced hypotension resulted in a narrow R-R interval variation range in LTOT fetuses; Cntl fetuses showed early breakdown in compensation. Baroreflex response slope during PE-induced fetal hypertension was lower in LTOT than in Cntl fetuses. Although the cortisol-to-ACTH ratio was lower in LTOT fetuses, fetal plasma ACTH and cortisol changes were similar in control and LTOT fetuses. We hypothesize that contracture-induced alterations in the intrauterine environment accelerate fetal cardiovascular development through mild hypoxemia, repetitive fetal pituitary-adrenal stimulation, and/or physical stimulation.

Retinoic acid selectively activates the ERK2 but not JNK/SAPK or p38 MAP kinases when inducing myeloid differentiation

Among the three major mitogen-activated protein kinase (MAPK) cascades--the extracellular signal regulated kinase (ERK) pathway, the c-JUN N-terminal/stress-activated protein kinase (JNK/SAPK) pathway, and the reactivating kinase (p38) pathway--retinoic acid selectively utilizes ERK but not JNK/SAPK or p38 when inducing myeloid differentiation of HL-60 human myeloblastic leukemia cells. Retinoic acid is known to activate ERK2. The present data show that the activation is selective for this MAPK pathway. JNK/SAPK or p38 are not activated by retinoic acid. Presumably because it activates relevant signaling pathways including MAPK, the polyoma middle T antigen, as well as certain transformation defective mutants thereof, is known to promote retinoic acid-induced differentiation, although the mechanism of action is not well understood. The present results show that consistent with the selective involvement of ERK2, ectopic expression of either the polyoma middle T antigen or its dl23 mutant, which is defective for PLCgamma and PI-3 kinase activation, or the delta205 mutant, which in addition is also weakened for activation of src-like kinases, caused no enhanced JNK/SAPK or p38 kinase activity that promoted the effects of retinoic acid. However, all three of these polyoma antigens are known to enhance ERK2 activation and promote differentiation induced by retinoic acid. Polyoma-activated MAPK signaling relevant to retinoic acid-induced differentiation is thus restricted to ERK2 and does not involve JNK/SAPK or p38. Taken together, the data indicate that among the three parallel MAPK pathways, retinoic acid-induced HL-60 myeloid differentiation selectively depends on activating ERK but not the other two MAPK pathways, JNK/SAPK or p38, with no apparent cross talk between pathways. Furthermore, the striking ability of polyoma middle T antigens to promote retinoic acid-induced differentiation appears to utilize ERK, but not JNK/SPK or p38 signaling.

Level of postoperative analgesia is a critical factor in regulation of myometrial contractility after laparotomy in the pregnant baboon: implications for human fetal surgery

OBJECTIVES

We used 2 dosage levels of postoperative opioid administration to determine whether the degree of postoperative analgesia after laparotomy during the last third of baboon pregnancy alters maternal pituitary-adrenal function, androgen secretion, and placental estrogen production. We also determined the relationship of estrogen production to surgery-induced increase in myometrial contraction activity.

STUDY DESIGN

After laparotomy under halothane general anesthesia at 0.75 gestation, 10 pregnant baboons were administered intra-arterially either a normal dose or a double dose of the opioid analgesic buprenorphine for 48 hours. Maternal plasma samples for steroid hormone and oxytocin analyses were obtained at circadian time 1000 hours and at circadian time 1800 hours, 4 hours before and 4 hours after the lights went off, respectively. Myometrial electromyographic contraction activity was quantified for the 6 hours from circadian time 1100 hours to circadian time 1700 hours.

RESULTS

Maternal plasma cortisol and dehydroepiandrosterone sulfate concentrations were lower in the dark period (at circadian time 1800 hours) than during daylight (at circadian time 1000 hours) in the double-dose group but not the normal dose group. In contrast, maternal plasma estradiol level was higher at circadian time 1800 hours than at circadian time 1000 hours in the normal dose group but not in the double-dose group. Maternal plasma estrogen level was higher during the hours of darkness in the normal dose group than in the double-dose group. Furthermore the number of myometrial contractions around the onset of darkness was greater in the normal dose group than in the double-dose group.

CONCLUSIONS

The double dose of analgesia results in lower maternal nighttime plasma estradiol concentrations and significantly less nocturnal contraction activity. These observations further confirm an association between increased maternal plasma estrogen concentrations and increased myometrial contractility in the nonhuman primate. In addition, they suggest that adjustment of the level of postoperative analgesia may be of importance in preventing premature labor after chuman intrauterine fetal surgery.

Alteration of fetal oxygenation and responses to acute hypoxemia by increased myometrial contracture frequency produced by pulse administration of oxytocin to the pregnant ewe from 96 to 131 days' gestation

OBJECTIVES

This study examined the effects of increased myometrial contracture frequency from 96 to 131 days' gestation on ovine fetal oxygen transport and physiologic response to acute hypoxemia.

STUDY DESIGN

Ten pregnant ewes received either saline solution (control, n = 5) or long-term administration of oxytocin (600 microU. kg-1. min-1) in 5-minute pulses every 20 minutes to the maternal jugular vein beginning at 96 days' gestation (n = 5). Maternal tracheal tubes, fetal carotid artery and jugular vein catheters, and electrocorticographic and electromyographic electrodes were placed with the animals under halothane general anesthesia at 122 days' gestation. At 131 days' gestation fetal hypoxemia was induced for 1 hour. Maternal and fetal arterial blood gas samples were obtained at 60, 15, and 5 minutes before the start of hypoxemia and at 5, 10, 20, 30, 40, 60, and 120 minutes after the start of hypoxemia.

RESULTS

Baseline PO2 before hypoxemia was significantly lower and oxygen content was significantly higher in fetuses in the long-term oxytocin group than in control fetuses. At the end of hypoxemia the fetal pH, oxygen saturation, and oxygen content were significantly higher in the long-term oxytocin group than in the control group, although PO2 did not differ between groups. The fetal blood oxygen dissociation curve was shifted to the left in the long-term oxytocin group. During hypoxemia the absolute fetal blood pH was higher and the blood pH variation was lower in long-term oxytocin group than in the control group. Lower baseline and hypoxia-induced fetal plasma cortisol concentrations were observed in fetuses in the long-term oxytocin group than in fetuses of control ewes.

CONCLUSION

Increased contracture frequency during a period of 35 days shifts the fetal oxygen dissociation curve toward the left and alters fetal response to acute hypoxemia.

Transformation-defective polyoma middle T antigen mutants defective in PLCgamma, PI-3, or src kinase activation enhance ERK2 activation and promote retinoic acid-induced, cell differentiation like wild-type middle T

In HL-60 human myeloblastic leukemia cells, retinoic acid is known to cause cFMS, RAF, MEK, and ERK2 dependent myeloid cell differentiation and G0 arrest associated with RB tumor suppressor protein hypophosphorylation, implicating receptor tyrosine kinase signal transduction in propelling these retinoic acid-induced cellular effects. Furthermore, ectopic expression of polyoma middle T antigen, which activates similar early signal transduction molecules as PDGF class receptors such as cFMS, accelerates these retinoic acid-induced effects. To determine if this depends on middle T's ability to activate PLCgamma, PI-3 kinase, and src-like kinases, stable transfectants of HL-60 cells expressing either the polyoma middle T dl23 mutant, which is defective for PLCgamma and PI-3 kinase activation, or the Delta205 mutant, which in addition has greatly attenuated src-like kinase activation ability, were created and compared to wild-type middle T-transfected HL-60. The transgenes were under control of the retinoic acid (or 1, 25-dihydroxy vitamin D3) inducible Moloney murine leukemia virus LTRs. Expression of the dl23 or Delta205 mutant accelerated retinoic acid-induced cell differentiation. The effects of the mutants were comparable to those of the wild-type middle T. Likewise, retinoic acid-induced G0 arrest of mutant transfected cells and wild-type middle T transfected cells was similar. The same was true for 1, 25-dihydroxy vitamin D3-induced monocytic differentiation as for retinoic acid-induced myeloid differentiation. The mutants did not cause the same slight shortening of the cell cycle as wild-type middle T. Both the mutants and the wild-type middle T caused a similar increase in the cellular basal level of activated ERK2 MAPK. Since retinoic acid increases ERK2 activation, which is necessary for differentiation, the data suggest that mutant and wild-type middle T enhanced the retinoic acid effects by increasing basal levels of ERK2 activation. Consistent with this, the polyoma-induced foreshortening of the time for differentiation coincided with the time for retinoic acid to significantly increase ERK2 activation. As in wild-type HL-60, retinoic acid induced the early down-regulation of RXRalpha in mutant transfectants similar to wild-type middle T transfectants, consistent with no loss or gain of relevant functions due to the mutations. In contrast, vitamin D3 did not down-regulate RXRalpha in HL-60 or transfectants. Polyoma middle T and these transformation-defective mutants thus enhanced ERK2 activation to have an early effect in promoting retinoic acid-induced differentiation without a strong dependence on activating PLCgamma, PI-3 kinase, or src-like kinase.

Regulation of MCL1 through a serum response factor/Elk-1-mediated mechanism links expression of a viability-promoting member of the BCL2 family to the induction of hematopoietic cell differentiation

Proliferation, differentiation, and apoptosis are tightly regulated during hematopoiesis, allowing amplification along specific lineages while preventing excessive proliferation of immature cells. The MCL1 member of the BCL2 family is up-regulated during the induction of monocytic differentiation (approximately 10-fold with 12-O-tetradecanoylphorbol 13-acetate (TPA)). MCL1 has effects similar to those of BCL2, up-regulation promoting viability, but differs from BCL2 in its rapid inducibility and its pattern of expression. Nuclear factors that regulate MCL1 transcription have now been identified, extending the previous demonstration of signal transduction through mitogen-activated protein kinase. A 162-base pair segment of the human MCL1 5'-flank was found to direct luciferase reporter activity, allowing approximately 10-fold induction with TPA that was suppressible upon inhibition of the extracellular signal-regulated kinase (ERK) pathway. Serum response factor (SRF), Elk-1, and Sp1 bound to cognate sites within this segment, SRF and Elk-1 acting coordinately to affect both basal activity and TPA inducibility, whereas Sp1 affected basal activity only. Thus, the mechanism of the TPA-induced increase in MCL1 expression seen in myelomonocytic cells at early stages of differentiation involves signal transduction through ERKs and transcriptional activation through SRF/Elk-1. This finding provides a parallel to early response genes (e.g. c-FOS and EGR1) that affect maturation commitment in these cells and therefore suggests a means through which enhancement of cell viability may be linked to the induction of differentiation.

Involvement of the 5' proximal coding sequences of hepatitis C virus with internal initiation of viral translation

The 5' nontranslated region (NTR) of hepatitis C virus (HCV) consists of 341 nucleotides (nt). This region comprises the majority of the internal ribosome entry site (IRES) which controls the efficiency of viral translation. Previous studies of the 3' boundary of the HCV IRES yielded conflicting data regarding the involvement of viral coding sequences in IRES activity. We therefore studied the functional significance of the 5' proximal coding sequences of the HCV core gene on IRES activity. We constructed monocistronic and bicistronic DNAs that contained either a chloramphenicol acetyl transferase (CAT) gene or a luciferase (Luc) gene as the reporter. Results from both in vitro and in vivo experiments indicated that the optimal IRES ranged within nt 1-371. Further mutational analyses of sequences surrounding the initiation codon revealed that primary sequences downstream of the AUG initiator rather than the secondary structure are important in regulating optimal IRES function. We are also able to demonstrate that a non-AUG codon could be used to initiate the synthesis of a reporter protein, albeit with lower efficiency. These findings bear important implications for the HCV IRES secondary structures.

Retinoic acid induced mitogen-activated protein (MAP)/extracellular signal-regulated kinase (ERK) kinase-dependent MAP kinase activation needed to elicit HL-60 cell differentiation and growth arrest

Retinoic acid (RA) activated the extracellular signal-regulated kinase (ERK) 2 mitogen-activated protein kinase (MAPK) of HL-60 human myeloblastic leukemia cells before causing myeloid differentiation and cell cycle arrest associated with hypophosphorylation of the retinoblastoma (RB) tumor suppressor protein. ERK2 activation by mitogen-activated protein/ERK kinase (MEK) was necessary for RA-induced differentiation in studies using PD98059 to block MEK phosphorylation. G0 growth arrest and RB tumor suppressor protein hypophosphorylation (which is typically associated with induced differentiation and G0 arrest), two putatively RB-regulated processes, also depended on ERK2 activation by MEK. Activation of ERK2 by RA occurred within hours and persisted until the onset of RB hypophosphorylation, differentiation, and arrest. ERK2 activation was probably needed early, because delaying the addition of PD98059 relative to that of RA restored most of the RA-induced cellular response. In contrast to RA (which activates RA receptors (RARs) and retinoid X receptors in HL-60 cells with its metabolite retinoids), a retinoid that selectively binds RAR-gamma, which is not expressed in HL-60 cells, was relatively ineffective in causing ERK2 activation. This is consistent with the need for a nuclear retinoid receptor function in RA-induced ERK2 activation. RA reduced the amount of unphosphorylated RAR-alpha, whose activation is necessary for RA-induced differentiation and arrest. This shifted the ratio of phosphorylated:unphosphorylated RAR-alpha to predominantly the phosphorylated form. Unlike other steroid thyroid hormone receptors susceptible to phosphorylation and activation by MAPKs, RAR-alpha was not phosphorylated by the activated ERK2 MAPK. The results thus show that RA augments MEK-dependent ERK2 activation that is needed for subsequent RB hypophosphorylation, cell differentiation, and G0 arrest. The process seems to be nuclear receptor dependent and an early seminal component of RA signaling causing differentiation and growth arrest.

Preliminary X-ray crystallographic study of wild-type and mutant ribulose-1,5-bisphosphate carboxylase/oxygenase from Chlamydomonas reinhardtii

Ribulose-1,5-bisphosphate carboxylase/oxygenase is the key enzyme for photosynthesis. The wild-type and mutant (amino-acid substitutions in the catalytically important loop 6 region) enzymes from Chlamydomonas reinhardtii, a unicellular green alga, were crystallized. Wild-type, single-mutant (V331A) and two double-mutant (V331A/T342I and V331A/G344S) proteins were activated with cofactors CO2 and Mg2+, complexed with the substrate analog 2'-carboxyarabinitol-1,5-bisphosphate, and crystallized in apparently isomorphous forms. Unit-cell determinations have been completed for three of the enzymes. They display orthorhombic symmetry with similar cell parameters: wild type a = 130.4, b = 203. 3, c = 208.5 A; single mutant (V331A) a = 128.0, b = 203.0, c = 207. 0A; and double mutant (V331A/T342I) a = 130.0, b = 202.1, c = 209.7 A. Crystals of the wild-type and single-mutant (V331A) enzymes diffracted to approximately 2.8 A. A small crystal of the double-mutant (V331A/T342I) enzyme diffracted to approximately 6 A. A partial data set (68% complete) of the wild-type protein has been collected at room temperature to about 3.5 A.

Hypophosphorylation of the RB protein in S and G2 as well as G1 during growth arrest

The RB tumor suppressor protein is a cell cycle regulator, where hypophosphorylated RB is associated with G1/0 arrest and its cyclin-dependent phosphorylation in G1 allows progression from G1 to S. The present report shows that in human leukemia cells induced to undergo growth arrest with sodium butyrate or DMSO, hypophosphorylation of the RB protein is not G1 restricted and also occurs in S and G2/M cells as well as in G1 cells when growth is inhibited. While all of the RB protein in G1/0 cells is hypophosphorylated, residual cells in S and G2 have significant detectable amounts of hypophosphorylated RB as well as still hyperphosphorylated RB protein. Thus RB hypophosphorylation can be induced in S and G2 as well as the G1 phase. The results show that growth retardation in other than the G1 phase is associated with occurrence of hypophosphorylated RB. RB may thus have a broader capability to inhibit proliferation than just in G1.

Detection of human herpesvirus-8 DNA in Kaposi's sarcomas from iatrogenically immunosuppressed patients

BACKGROUND

Kaposi's sarcoma (KS) accounts for more than 5% of malignancies in immunosuppressed organ transplant patients (OKS). A new herpesvirus (HHV-8) was identified with high prevalence in biopsy specimens of AIDS-KS, endemic KS, and classic KS and in OKS. KS has also been associated with other underlying diseases in patients treated with corticosteroids, but this subset of KS has been reported to contain HHV-8 in only a few case reports.

OBJECTIVE

In this larger study, we determined the prevalence of HHV-8 in seven patients of Jewish origin in whom KS developed during immunosuppressive therapy for different primary diseases (ISKS).

METHODS

The study included HHV-8 DNA detection by polymerase chain reaction (PCR) coupled with Southern blot and sequence analysis as well as by in situ hybridization.

RESULTS

HHV-8 sequences were detected by PCR with confirmation by Southern blot and sequence analysis in 100% of the ISKS samples. Direct sequencing revealed several previously unknown base changes within the 208 bp region from open reading frame 26 (ORF26[208]) of HHV-8 in ISKS.

CONCLUSION

Ours is the largest known study describing the presence of HHV-8 in iatrogenic KS from immunosuppressed nontransplant patients and provides data of previously unknown sequence variations within the ORF26 of HHV-8 DNA.

Polyoma middle T antigen in HL-60 cells accelerates hematopoietic myeloid and monocytic cell differentiation

Expression of the polyoma virus middle T antigen in HL-60 cells accelerates their differentiation in response to both monocytic and granulocytic differentiation-inducing agents. Middle T-expressing cells treated with the granulocytic inducer retinoic acid or the monocytic inducer 1,25-dihydroxy vitamin D3 differentiated 24 h earlier than parental, mock-electroporated, or vector control cell lines. The rapid onset of differentiation correlated with an increase in the cellular level of the middle T protein as well as two known retinoic-acid-inducible markers in HL-60 cells: the paxillin and transglutaminase gene products. The accelerated functional differentiation response and expression of retinoic-acid-inducible markers indicate that middle T played a causal role in differentiation. Thus, expression of the polyoma middle T antigen in HL-60 cells enhanced a variety of molecular changes associated with cellular differentiation.

Failure to detect human papilloma virus in cutaneous molluscum contagiosum lesions

In a recently published study, the coexistence of HPV and MCV was demonstrated for the first time in the same molluscum contagiosum lesions from a single patient. Such a finding raises many questions in the understanding of both HPV and MCV. With this finding comes the potential of new treatments against dually infected MC lesions, which normally demonstrate high resistance to therapy. Furthermore, the finding of HPV and MCV coexistence raises questions on the effects of MCV immunosuppressive genes on HPV. For these reasons, further analysis was performed on a larger series of MC specimens for the rates of HPV and MCV coinfection within the same lesions. This study differed from the previous one on this subject in its use of cutaneous, rather than mucosal, lesions. The methods used in this study were identical to those which were previously employed; in situ hybridization was utilized using HPV probes, and was followed by histologic examination with hematoxylin-eosin stain. The results of this study did not identify coexistence of HPV and MCV in any of the collected MC specimens. These findings are in contrast to the previous study and suggest that, although HPV and MCV coexistence may occur, such coinfections are extremely rare in cutaneous tissue.

Mid-dermal elastolysis in an adolescent subsequent to lesions resembling granuloma annulare

First described by Shelley and Wood in 1977, mid-dermal elastolysis (MDE) is a rare acquired disorder in which there is a bandlike absence of elastic tissue limited to the mid-dermis. In their patient, MDE developed in an area previously involved with recurrent episodes of urticaria. We describe a 15-year-old white girl with well-circumscribed, minimally palpable yellow-white plaques and wrinkling diagnosed histologically as MDE in areas clinically diagnosed 5 years previously as granuloma annulare. As in the first described patient, five years elapsed between clearance of the original skin lesions and the clinical appearance of MDE. To our knowledge, we report the first adolescent case of MDE localized to previous sites of lesions clinically consistent with granuloma annulare and propose that MDE represents an abnormal end-stage reaction to multiple processes.

Human herpesvirus 8 DNA sequences in blistering skin from patients with pemphigus

BACKGROUND

Human herpesvirus 8 (HHV-8) has been detected in Kaposi sarcoma (KS) and other lesions in patients both seropositive and seronegative for the human immunodeficiency virus (HIV). Kaposi sarcoma has been reported to develop in a disproportionate number of patients with pemphigus. Since HHV-8 is so strongly associated with KS, we wondered whether HHV-8 is present in pemphigus lesions from patients without KS or HIV infection. Pemphigus lesions and skin from healthy individuals were coded in a blinded fashion. Tissue-extracted DNA was tested using polymerase chain reaction, Southern blot hybridization, and automated sequencing of the polymerase chain reaction products for the presence of HHV-8 DNA. Six patients had pemphigus foliaceus, 6 had pemphigus vulgaris, and 2 had KS; 10 healthy individuals were used as controls. All 24 patients were HIV seronegative.

OBSERVATION

Lesional skin from 4 of the 6 patients with pemphigus vulgaris, all 6 of the patients with pemphigus foliaceus, and both positive controls (KS) tested positive for HHV-8 DNA. Furthermore, the HHV-8 DNA sequences for KS330(233) differed between all 6 DNA specimens from pemphigus foliaceus, while 3 of the 4 DNA specimens from pemphigus vulgaris were identical. However, HHV-8 DNA was absent in all normal human skin analyzed.

CONCLUSIONS

This report expands the spectrum of lesions found to contain HHV-8 DNA sequences and suggests that HHV-8 might have trophism for pemphigus lesions.

Mucoepidermoid carcinoma with cutaneous presentation

Mucoepidermoid carcinomas are malignant neoplasms that rarely involve the skin. Composed of both mucus-secreting cells and epidermoid-type cells in various proportions, mucoepidermoid carcinomas occur most commonly in salivary glands. In this case report, we describe a high-grade mucoepidermoid carcinoma with cutaneous involvement. Although this patient was referred for Mohs' micrographic surgery, further evaluation showed either direct or metastatic extension from the parotid gland to skin and distant metastases to the lung and bone. Despite extensive bone involvement, serum levels of ionized calcium, phosphorus, and lactate dehydrogenase remained normal. In view of the widespread metastases, the treatment plan was altered to radiotherapy and chemotherapy instead of surgery. Instructive lessons from this case include the recognition by dermatologists of this rare entity, the importance of a detailed history and complete evaluation of the patient before determining appropriate therapy, and the necessity of individualizing diagnostic tests to a particular patient.

An RXR-selective analog attenuates the RAR alpha-selective analog-induced differentiation and non-G1-restricted growth arrest of NB4 cells

NB4, a human acute promyelocytic leukemia cell line expressing the promyelocyte-retinoic acid receptor alpha (PML-RAR alpha) hybrid protein was treated with RAR- and retinoid X receptor (RXR)-selective analogs to determine their effects on cell proliferation, retinoblastoma (RB) tumor-suppressor protein phosphorylation, and differentiation. An RAR- or just RAR alpha-selective analog alone induced similar cell population growth arrest, cell cycle arrest without restriction to G1, hypophosphorylation of RB, and myelomonocytic cell surface differentiation marker expression (CD11b). In addition, an RAR alpha antagonist could inhibit the effects of the RAR alpha agonist completely. The RAR alpha-selective analog-elicited response was attenuated by simultaneous addition of various RXR-selective analogs. In contrast, each of the RXR-selective analogs was unable to induce any of the cellular responses analyzed. The growth arrest of NB4 cells is not G1-restricted and occurs at all points in the cell cycle. Cells growth arrested by treatment with an RAR alpha-selective analog show primarily hypophosphorylated RB. When these cells are sorted into G1 or S + G2/M subpopulations by flow cytometry, hypophosphorylated RB protein was in G1 as well as S + G2/M cells. This suggests that the hypophosphorylated RB protein may be mediating the growth arrest of NB4 cells at all points in the cell cycle. These results are consistent with an involvement of PML-RAR alpha and/or RAR alpha in the transduction of the retinoid signal in NB4 cells.

Mycosis fungoides: an Australian experience

Analysis was undertaken of 107 patients with mycosis fungoides who presented to St. Vincent's Hospital, Melbourne, during 1977-95. The mean age at diagnosis (55 years) was significantly older than the mean age of onset of symptoms (48 years). The mean duration of follow-up was 7.7 years. Urban residence was over-represented in this group of patients and in those with mycosis fungoides recorded at the State Cancer Registry. Eighty-four per cent were diagnosed at Stage I or II of the disease. Presentation with disease more advanced than Stage I was more likely to be found in males. Disease localized only to the trunk accounted for 45% of all patients. The mean number of biopsies prior to diagnosis was 1.4 but two-thirds were diagnosed at first biopsy. Almost 85% of patients had as their initial treatment either PUVA (44.9%), topical steroids (20.6%) or topical nitrogen mustard (18.7%) and 57% received only one or two treatment modalities during the period of the study. Stage at presentation was not related to the likelihood of clearance following treatment, recurrence, progression to a more advanced stage of disease or survival.

Increasing c-FMS (CSF-1 receptor) expression decreases retinoic acid concentration needed to cause cell differentiation and retinoblastoma protein hypophosphorylation

Increasing the expression of c-FMS (colony-stimulating factor 1 receptor) by introduction of a transgene reduced the concentration of retinoic acid or 1,25-dihydroxy vitamin D3 needed to cause myeloid or monocytic cell differentiation and hypophosphorylation of the retinoblastoma tumor suppressor protein (RB) typically associated with cell cycle G0 arrest and differentiation of HL-60 human myelo-monoblastic precursor cells. The data are consistent with a model in which signals originating with retinoic acid and c-FMS integrate to cause differentiation, RB hypophosphorylation, and G0 arrest. Furthermore, these two signals can compensate for each other. Three HL-60 sublines described previously (A. Yen et al., Exp. Cell Res., 229: 111-125, 1996) expressing low (wild-type HL-60), intermediate, and high cell surface c-FMS were treated with various concentrations of retinoic acid. The lowest concentration tested, 10(-8) M, induced significant differentiation of only the high c-FMS-expressing cells, with no accompanying hypophosphorylated RB or G0 arrest. The low and intermediate c-FMS expressing cells showed no induced differentiation, hypophosphorylation of RB, or G0 arrest. A 10-fold higher retinoic acid concentration, 10(-1) M, induced significant differentiation of both intermediate and high c-FMS-expressing cells. It induced RB hypophosphorylation only in high c-FMS-expressing cells but with no accompanying G0 arrest in any of the cells. The highest retinoic acid concentration, 10(-6) M, elicited differentiation, hypophosphorylation of RB, and G0 arrest in low, intermediate, and high c-FMS-expressing cells. As the concentration of retinoic acid increased, cell differentiation, hypophosphorylation of RB, and G0 arrest were progressively elicited within this ensemble of cells with different c-FMS expression levels. Thus, for example, at the lowest concentration of retinoic acid, expression of high enough c-FMS still allowed differentiation. At higher concentrations, progressively less c-FMS was needed for differentiation. The apparent threshold for the sum of the retinoic acid plus c-FMS originated signals to elicit differentiation, hypophosphorylation of RB, and G0 arrest increased, in that order. Thus retinoic acid-induced cell differentiation, RB hypophosphorylation, and G0 arrest have different signal threshold requirements. 1,25-Dihydroxy vitamin D3, also a ligand for a member of the steroid thyroid hormone receptor superfamily, caused monocytic differentiation with a similar c-FMS dependency, indicating that these effects characterize both myeloid and monocytic differentiation.

p53, WAF1/CIP1 and mdm2 expression in skin lesions associated with human papillomavirus and human immunodeficiency virus

Human papillomaviruses (HPVs) express various gene products, such as E6 protein which complexes with the p53 tumor suppressor protein and therefore diminishes p53-related regulatory mechanisms. This interaction is assumed to be HPV type-specific as "high risk" or oncogenic HPV types have more affinity for p53 binding than their "low risk" or non-oncogenic counterparts. Furthermore, HIV infection is believed to activate latent HPV infection and transcription via direct and indirect interaction with HPVs as well as cellular genes and functions. Accordingly, we carried out experiments on biopsies which originated from condylomas ("low risk" HPVs), HIV-positive condylomas (infection with multiple "low risk" and "high risk" HPVs) and anogenital squamous cell carcinomas (SCCs, "high risk" HPV infection). Using reverse transcription PCR (RT-PCR) and western immunoblotting, mRNA and protein levels of p53 and genes regulated by p53, such as mdm2 and WAF1/CIP1 were determined. We found that the presence of HPV can diminish p53 and increase WAF1/CIP1 and mdm2 protein levels. There were no significant differences in this regulation between "low risk" and "high risk" lesions. Our data suggest that these HPV-mediated cellular effects are not type-specific, and they might be part of a viral-cell interaction or represent a cellular defense mechanism against the virus. However, HIV-seropositivity renders HPV lesions containing both "low risk" and "high risk" significantly different. This may be due to the alteration of HPV-controlling cellular pathways by HIV tat and/or activation of cellular pathways different from HIV-negative counterparts. Either possibility is of great interest and needs further verification.

EBV-associated Kikuchi's histiocytic necrotizing lymphadenitis with cutaneous manifestations

The clinical and pathologic findings of Kikuchi's histiocytic necrotizing lymphadenitis may mimic those of malignant lymphoma. We describe a 6-year-old boy with generalized lymphadenopathy, spiking fever, chills, myalgias, malaise, and erythematous, crusted papules. Although cutaneous manifestations have been noted in 16% to 40% of patients with histiocytic necrotizing lymphadenitis, only three publications described skin lesions. The skin lesions and affected lymph nodes revealed histiocytic aggregates, atypical lymphoid cells, karyorrhectic debris, and patchy necrosis. Spontaneous resolution occurred in 2 months. Results of serologic studies, Epstein-Barr virus (EBV) latent membrane protein immunoperoxidase staining, EBER-1 RNA in-situ hybridization, and EBV EBNA-1 DNA polymerase chain reaction implicate EBV as the causative agent.

Concentration of RB protein in nucleus vs. cytoplasm is stable as phosphorylation of RB changes during the cell cycle and differentiation

Unphosphorylated RB (retinoblastoma tumor suppressor) protein is known to bind isolated nuclear matrix in vitro, whereas phosphorylated RB has a lower affinity, suggesting a mechanism which might contribute to differential nuclear/cytoplasmic localization as part of its regulatory activity. This motivates interest in the in vivo localization of the endogenous RB protein as its phosphorylation state changes during the cell cycle and cell differentiation. It is known that in proliferating HL-60 cells all the RB protein is phosphorylated, but the extent of phosphorylation increases with progression from G1 to S to G2 + M. It has also been previously shown that retinoic acid and 1,25-dihydroxy vitamin D3 shift the RB protein to the unphosphorylated state with cell differentiation (Yen, A., S. Varvayanis, Exp. Cell Res. 214, 250-257 (1994)). The dependence of cell cycle progression and differentiation on RB nuclear versus cytoplasmic localization, as well as the dependence of RB localization on phosphorylation state can thus be tested. Confocal image analysis of the RB protein in vivo shows that the ratio of the concentration of the RB tumor suppressor gene protein in the nucleus versus the cytoplasm remains stable as the RB protein undergoes either phosphorylation during cell cycle progression or dephosphorylation during cell differentiation induced by retinoic acid or 1,25-dihydroxy vitamin D3. For the cell cycle analysis, HL-60 human promyelocytic leukemia cells were fluorescently stained for DNA and for the RB protein. G1, S, and G2 + M subpopulations were isolated by fluorescence-activated cell sorting. For each subpopulation, the relative concentration of RB protein in the nucleus and the cytoplasm was measured by laser confocal image analysis. To determine the effect of retinoic acid-induced myeloid differentiation or 1,25-dihydroxy vitamin D3-induced monocytic differentiation, the same cell sorting and image analysis was performed on cells treated with these inducers. In all cases the concentration of the RB protein in the nucleus was approximately 2 times that in the cytoplasm. Thus, the ratio of nuclear versus cytoplasmic RB protein concentration is stable and independent of phosphorylation or dephosphorylation of RB during both the cell cycle and cell differentiation.

FMS (CSF-1 receptor) prolongs cell cycle and promotes retinoic acid-induced hypophosphorylation of retinoblastoma protein, G1 arrest, and cell differentiation

The effect of the CSF-1 receptor, cFMS, on the phosphorylation of the retinoblastoma (RB) tumor suppressor protein and on the cell cycle and cell differentiation was analyzed in a cultured promyelocytic leukemia cell capable of induced myelomonocytic differentiation. A series of cFMS-transfected HL-60 sublines with progressively higher cell surface FMS expression was derived by flow cytometric cell sorting. Overexpression of FMS increased the duration of the cell cycle, prolonging all cell cycle phases especially S phase, which doubled. The increased cell cycle generation times occurred without any detectable changes in RB expression level or phosphorylation. For retinoic acid (RA)-induced myeloid differentiation, progressive overexpression of FMS caused a greater fraction of cells to differentiate and G1/0 arrest compared to wild-type cells after the same number of cell cycle generation times. FMS overexpression also progressively increased the relative amount of dephosphorylated RB protein induced, while reducing the total amount of RB protein. The inducer-originated and FMS-driven changes in RB hypophosphorylation were not effected through changes in p21/WAF1/CIP1 in this p53-negative cell. Similar effects on differentiation and G0 arrest occurred with 1,25-dihydroxy vitamin D3 (D3)-induced monocytic differentiation. FMS did not significantly affect myeloid differentiation induced by DMSO, which does not target steroid-thyroid hormone receptors like RA and D3. While differentiation is typically associated with hypophosphorylated RB in all these cases, the kinetics indicate that the FMS-induced changes in cell cycle and cell differentiation do not depend in a direct causal fashion on the interconversion between hyperphosphorylated and hypophosphorylated RB.

Congenital smooth muscle hamartoma presenting as a linear atrophic plaque: case report and review of the literature

Congenital smooth muscle hamartoma usually manifests as a well-circumscribed, hyperpigmented plaque, frequently hypertrichotic, on the trunk or extremities. We report such a lesion in a 7-month-old girl that presented as a linear, mottled, purplish red plaque appearing in areas to be atrophic, involving her right buttock, posterior thigh and leg, and fifth toe. Although the clinical appearance suggested linear morphea, a biopsy specimen had numerous haphazardly oriented bundles of smooth muscle in the reticular dermis. Masson trichrome staining, smooth muscle specific actin, and electron microscopic studies confirmed the smooth muscle nature of the cells. A diagnosis of smooth muscle hamartoma was made. To our knowledge, this linear clinical presentation has not been described previously.

Retinoic acid-induced RB (retinoblastoma) hypophosphorylation enhanced by CGP 52411 (4,5-dianilinophthalimide), an EGF family tyrosine kinase receptor inhibitor

Retinoic acid is a known morphogen which can regulate cell proliferation and differentiation and also induces the hypophosphorylation of the RB (retinoblastoma tumor suppressor gene) protein, a known cell cycle regulatory protein. The mechanism by which these processes occur is unclear. We find that these processes can be regulated by CGP 52411, 4,5-dianilinophthalimide, an inhibitor of tyrosine protein kinases of the EGF receptor subfamily. Retinoic acid causes the largely phosphorylated RB protein expressed in proliferating HL-60 human promyelocytic leukemia cells to shift to the unphosphorylated form, as well as causing the cells to G0 arrest and differentiate. Addition of CGP 52411 accelerated the redistribution of the RB protein expressed in HL-60 cells to the unphosphorylated form, enhancing the effects of the retinoic acid. By itself CGP 52411 had no apparent effect on the RB protein expressed in HL-60 cells. CGP 52411 also accelerated the retinoic acid-induced accumulation of cells in G1/0 and the phenotypic conversion of cells to the mature myeloid phenotype, suggesting that its target is common to the regulation of both RB phosphorylation and cell proliferation and differentiation. CGP 52411 had a similar effect on the RB phosphorylation shift induced by 1,25-dihydroxy vitamin D3, a ligand for a receptor in the same steroid thyroid hormone superfamily as retinoic acid. Increasing the concentration of CGP 52411 enhanced the acceleration of RB hypophosphorylation in the case of both retinoic acid and 1,25-dihydroxy vitamin D3. The data are consistent with the negative regulation of retinoic acid induced RB protein dephosphorylation coupled to cell cycle arrest and differentiation by a receptor tyrosine kinase sensitive to CGP 52411.

Leukemia cutis: Darier's sign in a neonate with acute lymphoblastic leukemia

Infantile leukemia accounts for only 3% of childhood leukemia. Leukemia cutis occurs in 25% to 30% of infants with congenital leukemia and is more frequently associated with acute myeloid leukemia than with acute lymphoblastic leukemia. We describe an infant in whom hyperpigmented macules that developed when the patient was 2 weeks old demonstrated Darier's sign when he was 4 weeks old. Acute lymphoblastic leukemia, early pre-B-cell type, was diagnosed when the patient was 10 weeks old. Examination at that age revealed 1 to 2 cm, firm, mildly tender nodules clustered on the scalp, face, and extremities, less severe involvement of the trunk, and marked induration of the face and eyelids. Darier's sign was elicited from the less infiltrated truncal lesions. Histologic examination revealed a dense monomorphous infiltrate consisting of pleomorphic, undifferentiated cells. No mast cells were revealed by Giemsa staining. This case is to our knowledge the first reported example of leukemia cutis demonstrating Darier's sign.

Myeloid differentiation and retinoblastoma phosphorylation changes in HL-60 cells induced by retinoic acid receptor- and retinoid X receptor-selective retinoic acid analogs

The ability of subtypes of retinoic acid receptors (RARs) and retinoid X receptors (RXRs) singly and in combination to elicit myeloid differentiation, G1/0-specific growth arrest, and retinoblastoma (RB) tumor suppressor protein dephosphorylation was determined in the human myeloblastic leukemia cell line HL-60 using subtype-selective retinoic acid (RA) analogs. RA analogs that selectively bind only to RARs (Am580 and/or TTNPB) or to RXRs (Ro 25-6603, SR11237, and/or SR11234) did not elicit the above-mentioned three cellular responses. In contrast, simultaneous treatment with both an RAR-selective ligand (Am580 or TTNPB) and an RXR-selective ligand (Ro 25-6603, SR11237, or SR11234) induced all three cellular processes. An RAR alpha-selective ligand used with an RXR-selective ligand generated the same responses as did all-trans RA or 9-cis RA, which affect both families of receptors, suggesting an important role for RAR alpha among RAR subtypes in eliciting cellular response. Consistent with this finding, the RAR alpha antagonist, Ro 41-5253, reduced the level of the cellular responses elicited by treatment with an RAR alpha-selective ligand plus RXR-selective ligand. The coupling of the shift of RB to its hypophosphorylated form with G1/0 arrest and differentiation in response to ligands is consistent with a possible role of RB as a downstream target or effector of RAR alpha and RXR in combination.