Nuclear localization of 68 kDa calmodulin-binding protein is associated with the onset of DNA replication

Nuclear Folate Metabolism

Despite unequivocal evidence that folate deficiency increases risk for human pathologies, and that folic acid intake among women of childbearing age markedly decreases risk for birth defects, definitive evidence for a causal biochemical pathway linking folate to disease and birth defect etiology remains elusive. The de novo and salvage pathways for thymidylate synthesis translocate to the nucleus of mammalian cells during S- and G2/M-phases of the cell cycle and associate with the DNA replication and repair machinery, which limits uracil misincorporation into DNA and genome instability. There is increasing evidence that impairments in nuclear de novo thymidylate synthesis occur in many pathologies resulting from impairments in one-carbon metabolism. Understanding the roles and regulation of nuclear de novo thymidylate synthesis and its relationship to genome stability will increase our understanding of the fundamental mechanisms underlying folate- and vitamin B₁₂-associated pathologies.

Role of androgen receptor in progression of LNCaP prostate cancer cells from G1 to S phase

Background

The androgen receptor (AR) plays a critical role in the proliferation of prostate cancer cells. However, its mechanism of action in proliferation remains unknown. An understanding of the mechanism of AR action in proliferation may lead to the development of effective strategies for the treatment of prostate cancer.

Methodology/Principal Findings

In this study we report that pulse treatment of synchronized LNCaP cells with Casodex, an AR-antagonist, for 4 hours in mid-G₁ phase was sufficient to prevent cells from entering S phase. Since the assembly of pre-replication complex (pre-RC) in G₁ is required for the progression of cells from G₁ to S phase, the effect of Casodex during mid-G₁ suggested that the role of AR in proliferation might be to regulate the assembly of pre-RC. To test this possibility, we investigated the interaction between AR and Cdc6, an essential component of pre-RC in LNCaP cells. AR co-localized and co-immunoprecipitated with Cdc6, and Casodex treatment disrupted this interaction. AR-immunoprecipitate (AR-IP) also contained cyclin E and cyclin A, which play a critical role in pre-RC assembly and cell cycle entry into S phase, and DNA polymerase-α, PCNA, and ribonucleotide reductase, which are essential for the initiation of DNA synthesis. In addition, in cells in S phase, AR co-sedimented with components of the DNA replication machinery of cells that entered S phase.

Conclusions/Significance

Together, these observations suggest a novel role of AR as a component of the pre-RC to exert control over progression of LNCaP cells from G₁ to S phase through a mechanism that is independent of its role as a transcription factor.

Role of Ca2+ activation and bilobal structure of calmodulin in nuclear and nucleolar localization

Ca2+ signalling to the nucleus is thought to occur by calmodulin entry into the nucleus where calmodulin has many functions. In the present study we have investigated the role of Ca2+ and the N- and C-terminal lobes of calmodulin in its subnuclear targeting by using fluorescently labelled calmodulin and its mutants and confocal microscopy. Our data show, first, that Ca2+ stimulation induces a reorganization of subnuclear structures to which apo-calmodulin can bind. Secondly, Ca2+-independent association of the C-terminal lobe is seen with subnuclear structures such as chromatin, the nuclear envelope and the nucleoli. Thirdly, Ca2+-dependent accumulation of both calmodulin and the C-terminal calmodulin lobe occurs in the nucleoli. The N-terminal lobe of calmodulin does not show significant binding to subnuclear structures although, similarly to the C-terminal lobe, it accumulates in the nucleoplasm of wheat germ agglutinin-blocked nuclei suggesting that a facilitated nuclear export mechanism exists for calmodulin.

Replitase: complete machinery for DNA synthesis

Replication of nuclear DNA in eukaryotes presents a tremendous challenge, not only due to the size and complexity of the genome, but also because of the time constraint imposed by a limited duration of S phase during which the entire genome has to be duplicated accurately and only once per cell division cycle. A challenge of this magnitude can only be met by the close coupling of DNA precursor synthesis to replication. Prokaryotic systems provide evidence for multienzyme and multiprotein complexes involved in DNA precursor synthesis and DNA replication. In addition, fractionation of nuclear proteins from proliferating mammalian cells shows co-sedimentation of enzymes involved in DNA replication with those required for synthesis of deoxynucleoside triphosphates (dNTPs). Such complexes can be isolated only from cells that are in S phase, but not from cells in G(0)/G(1) phases of cell cycle. The kinetics of deoxynucleotide metabolism supporting DNA replication in intact and permeabilized cells reveals close coupling and allosteric interaction between the enzymes of dNTP synthesis and DNA replication. These interactions contribute to channeling and compartmentation of deoxynucleotides in the microvicinity of DNA replication. A multienzyme and multiprotein megacomplex with these unique properties is called "replitase." In this article, we summarize some of the relevant evidence to date that supports the concept of replitase in mammalian cells, which originated from the observations in Dr. Pardee's laboratory. In addition, we show that androgen receptor (AR), which plays a critical role in proliferation and viability of prostate cancer cells, is associated with replitase, and that identification of constituents of replitase in androgen-dependent versus androgen-independent prostate cancer cells may provide insights into androgen-regulated events that control proliferation of prostate cancer cells and potentially offer an effective strategy for the treatment of prostate cancer.

Calmodulin-androgen receptor (AR) interaction: calcium-dependent, calpain-mediated breakdown of AR in LNCaP prostate cancer cells

Chemotherapy of prostate cancer targets androgen receptor (AR) by androgen ablation or antiandrogens, but unfortunately, it is not curative. Our attack on prostate cancer envisions the proteolytic elimination of AR, which requires a fuller understanding of AR turnover. We showed previously that calmodulin (CaM) binds to AR with important consequences for AR stability and function. To examine the involvement of Ca(2+)/CaM in the proteolytic breakdown of AR, we analyzed LNCaP cell extracts that bind to a CaM affinity column for the presence of low molecular weight forms of AR (intact AR size, approximately 114 kDa). Using an antibody directed against the NH(2)-terminal domain (ATD) of AR on Western blots, we identified approximately 76-kDa, approximately 50-kDa, and 34/31-kDa polypeptides in eluates of CaM affinity columns, suggesting the presence of CaM-binding sites within the 31/34-kDa ATD of AR. Under cell-free conditions in the presence of phenylmethylsulfonyl fluoride, AR underwent Ca(2+)-dependent degradation. AR degradation was inhibited by N-acetyl-leu-leu-norleu, an inhibitor of thiol proteases, suggesting the involvement of calpain. In intact cells, AR breakdown was accelerated by raising intracellular Ca(2+) using calcimycin, and increased AR breakdown was reversed with the cell-permeable Ca(2+) chelator bis-(O-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid tetra-(acetoxymethyl)-ester. In CaM affinity chromatography studies, the Ca(2+)-dependent protease calpain was bound to and eluted from the CaM-agarose column along with AR. Caspase-3, which plays a role in AR turnover under stress conditions, did not bind to the CaM column and was present in the proenzyme form. Similarly, AR immunoprecipitates prepared from whole-cell extracts of exponentially growing LNCaP cells contained both calpain and calpastatin. Nuclear levels of calpain and calpastatin (its endogenous inhibitor) changed in a reciprocal fashion as synchronized LNCaP cells progressed from G(1) to S phase. These reciprocal changes correlated with changes in AR level, which increased in late G(1) phase and decreased as S phase progressed. Taken together, these observations suggest potential involvement of AR-bound CaM in calcium-controlled, calpain-mediated breakdown of AR in prostate cancer cells.

Physical and functional interaction of androgen receptor with calmodulin in prostate cancer cells

Ca(2+) and calmodulin (CaM) play a critical role in proliferation and viability of a wide variety of cells, including prostate cancer cells. We examined two prostate cancer cell lines, androgen-sensitive LNCaP and androgen-independent PC-3. Proliferation of LNCaP cells was six to eight times more sensitive to the inhibitory effect of the CaM antagonist N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide hydrochloride (W-7) than were PC-3 cells. Because LNCaP cell proliferation is sensitive to stimulation by androgen, we assessed the physical and functional interaction between androgen receptor (AR) and CaM. We observed tight binding of AR to CaM when LNCaP cell extracts were subjected to CaM-affinity column chromatography. AR binding to CaM was Ca(2+)-dependent and was inhibited by pretreatment of the cell extracts with W-7. Using immunofluorescence staining and confocal microscopy, we demonstrated colocalization of AR and CaM in the nucleus of LNCaP cells. Furthermore, the functional relevance of AR-CaM interactions in intact cells was revealed by the observation that W-7 was as effective as Casodex, an antiandrogen, in blocking AR-regulated expression of prostate-specific antigen in LNCaP cells. AR seems to interact with CaM directly because purified human AR could bind to CaM-agarose, and CaM could be detected in AR-immunoprecipitate prepared from purified soluble proteins. These studies provide direct evidence for physical and functional interaction between AR and CaM and suggest the potential usefulness of CaM antagonists in blocking AR activity in prostate cancer.

Clinical significance of serum calcineurin in acute leukemia

BACKGROUND

Calcineurin is involved in T-lymphocyte activation as well as in the maturation of hematopoietic cells. Identification of this predominantly intracellular phosphatase and of calmodulin (CaM) in human sera warranted their assessment in different types of acute leukemias.

METHODS

Phosphatase activity of calcineurin (CaN) was assayed, involving the measurement of trifluoperazine-sensitive neutral phosphatase, in sera of leukemic patients before and after treatment. Calcineurin and calmodulin contents were also determined by ELISA employing monoclonal antibodies specific to the proteins.

RESULTS

The activity of calcineurin was decreased by 75% and 85% in sera of patients diagnosed either for acute lymphoid leukemia and acute myeloid leukemia, respectively, without apparent changes in calmodulin or calcineurin contents under both these conditions. In addition, the decreased calcineurin activity in acute myeloid leukemia was restored to levels comparable to non-leukemic individuals upon treatment. This was not observed in cases of acute lymphoid leukemia.

CONCLUSIONS

These results suggest diagnostic utility in the measurement of serum calcineurin activity in acute leukemia. Restoration of normal calcineurin activity in patients undergoing treatment for acute myeloid leukemia may provide a means to monitor patient response to the prescribed therapeutic regimen.

Calmodulin is essential for estrogen receptor interaction with its motif and activation of responsive promoter

Calmodulin (CaM) has been reported to have affinity for the estrogen receptor (ER). Observations reported here reveal a direct physical interaction between purified CaM and ER. This direct ER-CaM interaction may be an initial event preceding the assembly of ER plus auxiliary proteins into the active ER complex with its DNA motif, the estrogen response element. We demonstrate that CaM is an integral component of this complex by using a system reconstituted from purified ER and nuclear extract from ER-negative breast cancer cells and also with ER-depleted nuclear extract of an ER-positive breast cancer cell line. Although CaM is essential for formation of this complex, it is not sufficient, suggesting roles also of auxiliary proteins. CaM also is functionally required for activation of an ER-responsive promoter, in the 17beta-estradiol-ER pathway of hormone action and regulation of 17beta-estradiol-responsive gene expression that is associated with proliferation of mammary epithelial cells.

The role of calcium in the cell cycle: facts and hypotheses

The regulation of cell cycle progression is a complex process which involves kinase cascades, protease action, production of second messengers and other operations. Increasing evidence now compellingly suggests that changes in the intracellular Ca2+ concentration may also have a crucial role. Ca2+ transients occur at the awakening from quiescence, at the G/S transition, during S-phase, and at the exit from mitosis. They may lead to the activation of Ca2+ binding proteins like S-100, but the key decoder of the Ca2+ signals in the cycle is calmodulin. Activation of calmodulin leads to the stimulation of protein kinases, i.e., CaM-kinase II, and of the CaM-dependent protein phosphatase calcineurin. Ample evidence now indicates the G/S transition, the progression from G2 to M, and the metaphase/anaphase transition as specific points of intervention of CaM-kinase II. Another attractive possibility for the role of Ca2+ in the cycle is through the activation of the Ca(2+)-dependent protease calpain: other proteases (e.g., the proteasome) have been suggested to be responsible for the degradation of some of cyclins, which is essential to the progression of the cycle. One of the cyclins, however, (D1) is instead degraded by calpain, which has been shown to promote both mitosis and meiosis when injected into somatic cells or oocytes.

Immunocytochemical localization of calmodulin in PC12 cells and its possible interaction with histones

The subcellular localization of calmodulin, a multi-functional calcium-binding regulatory protein, was examined immunocytochemically in undifferentiated PC12 rat pheochromocytoma cells and cells differentiated with nerve growth factor (NGF) and dibutyryl cyclic AMP. In undifferentiated PC12 cells, diffuse immunostaining for calmodulin was observed in the cytoplasm, and weak, patch-like staining was found in the nucleus. In differentiated cells, intense immunostaining for calmodulin was observed in the cytoplasm, while nuclear immunostaining was still evident. Immunoreactivity for calmodulin was also observed along newly-formed neuritic processes, with strong staining in varicosity-like structures and growth cones. Using double-label immunochemistry, the relative intensity of immunostaining for calmodulin among the nuclei was found to correlate with the relative intensity of immunostaining for histones in the same nuclei. A comparison of a profile of 125I-calmodulin binding in the nuclear fraction from PC12 cells to that of immunoblotting for histones in the same fraction indicated that some of the histones are calmodulin-binding proteins in PC12 cells. These results show that the level and subcellular distribution of calmodulin are altered during the course of nerve cell differentiation and suggest the possibility that histones may function as major nuclear binding proteins for calmodulin.

The 68 kDa calmodulin-binding protein is tightly associated with the multiprotein DNA polymerase alpha-primase complex in HeLa cells

Calcium and its receptor protein calmodulin function in the regulation of proliferation of mammalian cells. A 68 kDa calmodulin-specific binding protein was shown previously to be associated with growth factor-dependent progression of a variety of mammalian cells from G1 to S phase and to stimulate DNA synthesis in permeabilized hematopoietic progenitor cells. In this report we show that the 68 kDa calmodulin-specific binding protein in HeLa cells is tightly associated with the DNA polymerase alpha-primase component of the 21S complex of enzymes for DNA synthesis. The 68 kDa calmodulin-binding protein and the DNA polymerase alpha-primase complex cofractionate during Q-Sepharose chromatography to isolate the 21S enzyme complex, native and denatured DNA-cellulose to dissociate the 21S complex, and DEAE-Bio-Gel chromatography to isolate the multiprotein DNA polymerase alpha-primase complex. The 68 kDa calmodulin-specific binding protein and DNA polymerase alpha also bind and coelute during affinity chromatography on calmodulin-agarose. They also coprecipitate with C10-agarose-linked monoclonal antibody SJK 132-20 to human DNA polymerase alpha. The tight association of the 68 kDa calmodulin-binding protein to the DNA polymerase alpha-primase complex supports a function for this protein in the regulation of DNA synthesis in vivo.

Calmodulin-dependent protein kinase II is required for G1/S progression in HeLa cells

Calmodulin (CaM) has been previously shown to be essential for cell cycle progression in eukaryotic cells, being required at the G1/S, G2/M, and metaphase-anaphase transitions. Little is known about the the specific CaM-dependent enzymes that mediate Ca2+/CaM signaling to affect cell proliferation. In this study we show that inhibition of calmodulin kinase II (CaMKII) in HeLa cells using the CaMKII inhibitor KN-93 causes cell cycle arrest, demonstrating that CaMKII is required for cell cycle progression. Detailed analysis of arrest cells suggests that CaMKII is required for the initiation of DNA synthesis. Cells treated with KN-93 arrest with a G1 DNA content, but with elevated cyclin-dependent histone H1 kinase activity, suggesting that CaMKII may act at a point very close to the onset of DNA synthesis in mammalian cells.

Calcium, calmodulin and cell cycle progression

Proliferation of mammalian cells both in vivo and in vitro is dependent upon physiological concentrations of extracellular Ca2+. Growth factor stimulation of quiescent cells at the G0/G1 border usually results in a rapid mobilization of Ca2+ from both intra- and extracellular pools. However, Ca2+ influx is also required for later phases of cell cycle transition, especially in the late G1 phase for initiation of DNA synthesis. Available evidence indicates that calmodulin plays the major and essential roles in the Ca(2+)-dependent regulation of cell proliferation. Ca2+ and calmodulin act at multiple points in the cell cycle, including the initiation of the S phase and both initiation and completion of the M phase. Ca2+ and calmodulin stimulate the expression of genes involved in the cell cycle progression, leading to activation of cyclin-dependent kinases p33cdk2 and p34cdc2. Ca2+ and calmodulin are also involved in activation of enzymes participating in nucleotide metabolism and DNA replication, as well as nuclear envelope breakdown and cytokinesis. Ca2+/calmodulin-dependent protein kinase II and protein phosphatase calcineurin are both involved in the Ca2+ and calmodulin-mediated signalling of growth regulation. As compared to normal cells, growth of transformed cells is independent of extracellular Ca2+ and much less sensitive to calmodulin antagonists, suggesting the existence of derangements in the Ca2+ and calmodulin-mediated growth regulation mechanisms.

Protein kinase C regulates calmodulin expression in NRK cells activated to proliferate from quiescence

We have investigated the levels of calmodulin protein and calmodulin mRNA species during proliferative activation of NRK cells. Cells activated to proliferate from quiescence started to replicate DNA at 15 h, reaching a maximum at 20 h after serum addition. The maximum of mitosis was observed at 24 h. Quiescent cells showed a calmodulin concentration of 1.5 ng/micrograms of protein. At 10 h after serum addition the amount of calmodulin started to increase, reaching values of 3.0 ng/micrograms of protein at 24 h. NRK cells expressed predominantly 3 species of calmodulin transcripts: the 1.7 kb from CaM I, the 1.4 kb from CaM II and the 2.3 kb from CaM III. The amount of all the 3 transcripts was low in quiescent cells and 10 h after activation the levels were already high, reaching a maximum around 20 h. At the latter time the amount of the 3 calmodulin mRNAs was 5-10-fold higher than in serum starved cells. Run-on experiments showed that at 20 h after activation the transcription rates of the 3 calmodulin genes were higher than in quiescent cells. The addition of protein kinase C inhibitors to the cultures blocked the increase of the calmodulin transcripts while inhibitors of protein kinase A did not have any effect. Moreover, the addition of submitogenic doses of phorbol 12-tetradecanoate induced the increase of all 3 calmodulin transcripts. These results indicate that protein kinase C regulates calmodulin expression when NRK cells are activated to proliferate.

Calmodulin concentrated at the osteoclast ruffled border modulates acid secretion

Osteoclasts mediate acid dissolution of bone for maintenance of serum [Ca2+] and for replacement of old bone in terrestrial vertebrates. Recent findings point to the importance of intracellular signals, particularly Ca2+, in osteoclast regulation. However, acid degradation of bone mineral subjects the osteoclast to uniquely high extracellular [Ca2+]. We hypothesized that this high calcium environment would affect calcium signalling mechanisms, and studied the calcium binding regulatory protein, calmodulin, in the osteoclast. Avian osteoclast bone resorption was inhibited 30% at 1 microM and 90% at 7 microM by the calmodulin antagonist trifluoperazine. Osteoclast bone attachment was not affected by 10 microM trifluoperazine. Quantitative immunofluorescence using fluorescein-labelled calmodulin monoclonal antibody showed a severalfold increase of calmodulin concentration in bone attached relative to plastic attached osteoclasts. Western blots confirmed this, showing two to threefold increased osteoclast calmodulin per milligram of cell protein in 3-day bone-attached vs. nonattached cells. Scanning confocal microscopy showed calmodulin polarization to areas of bone attachment. Electron micrographs with 9 nm colloidal gold labelling showed calmodulin in the acid secreting ruffled membrane. ATP-dependent acid transport in osteoclast membrane vesicles was inhibited by the calmodulin antagonist calmidazolium. This effect was reversed by addition of excess calmodulin, showing that the inhibition is specific. Vesicle acid transport inhibition reflects an approximately fourfold shift in the apparent Km for ATP of vesicular acid transport in the presence of the calmodulin antagonist. We conclude that calmodulin concentration and distribution is modified by bone attachment, and that osteoclastic acid secretion is calmodulin regulated.

Expression of calmodulin and calmodulin binding proteins in lymphoblastoid cells

Calmodulin is encoded in vertebrates by three different genes: CALM1, CALM2, and CALM3. We have examined the mRNAs expressed from these three genes in eight lines of human lymphoblastoid cells (Namalwa, Raji, Ramos, JY, Molt-4, Jurkat, CEM, and HPB-ALL). We found that all these cell lines (except Ramos) overexpressed CALM3 transcripts, which led to an increase of total CaM protein with respect to quiescent normal T lymphocytes. The nuclear concentration of calmodulin was measured in two of these lymphoblastoid cell lines (JY and HPB-ALL) and compared to quiescent and phytohemagglutinin-activated T lymphocytes. Activated lymphocytes showed a 2-fold increase of nuclear calmodulin with respect to quiescent cells, whereas in the two lymphoblastoid cell lines, nuclear calmodulin remained similar to that of quiescent cells. The levels of a calmodulin-binding protein of 150 kDa in the homogenates of the eight lymphoblastoid lines was found to be higher than those of quiescent and activated lymphocytes. Likewise, the amount of three calmodulin-binding proteins of 240, 200, and 170 kDa was also increased in several of the cell lines, but not in all of them. The 170-kDa protein was only expressed by activated lymphocytes and lymphoblastoid cells, suggesting that it could be specific for proliferating cells. In the nuclei of activated lymphocytes and lymphoblastoid cells, a decrease of a calmodulin-binding protein of 110 kDa and increases of three other of 240, 180 and 170 kDa were also detected.

Cell cycle: regulatory events in G1-->S transition of mammalian cells

A cell divides into two daughter cells by progressing serially through the precisely controlled G1, S, G2, and M phases of the cell cycle. The crossing of the G1/S border, which is marked by the initiation of DNA synthesis, represents commitment to division into two complete cells. Beyond this critical point no further external signals are required. We now have more comprehensive knowledge of the temporal sequence of systems at this key transition from G1 to S--growth factor responses, a cascade of kinase reactions, activation of cyclins and their associated kinases, and oncogene and tumor suppressor gene products. Furthermore, we know that the absolute requirement for calcium and the timing of events associated with calmodulin and the 68 kDa calmodulin-binding protein are consistent with overall Ca++/calmodulin control of all steps from the response to growth factors in G1 to DNA replication in S phase. We now have to sort out the inter-relationships of myriad control proteins and their relation to the Ca++/calmodulin-dependent controls--Which are causes? Which are effects? And which are parallel processes? The answers will be important, as they represent both a much deeper understanding of this key process of life and an important opportunity for improving therapeutic medicine.

The role of polybasic compounds in determining the tyrosyl phosphorylation of calmodulin by the human insulin receptor

A highly purified human insulin receptor preparation was shown to effect receptor autophosphorylation and the phosphorylation of poly(GluTyr) but not that of calmodulin. Addition of poly-L-lysine allowed for the stoichiometric tyrosyl phosphorylation of calmodulin in a dose-dependent fashion (EC50 approximately 83 nM) with the single target residue identified at tyr99. Higher concentrations of poly-L-lysine elicited the dose-dependent inhibition of calmodulin phosphorylation (IC50 approximately 0.7 microM) by a process which did not apparently involve either stimulation of calmodulin phosphatase activity or diminished receptor kinase activity. Polybasic substances such as poly-L-arginine, histone H1 and protamine sulphate all promoted calmodulin phosphorylation by the insulin receptor in a similar biphasic dose-dependent fashion. Poly-lysine's actions proved to lack stereo-specificity in that both the D- and L-forms were equally as effective. Reduction in the chain length of poly-L-lysine species attenuated their ability to promote calmodulin phosphorylation with L-lysine proving to be ineffective. Optimal promotion of calmodulin phosphorylation was achieved at an apparently constant ratio of calmodulin to poly-L-lysine of approximately 1:4 over a 100-fold range of calmodulin concentrations. Poly-L-lysine promoted the precipitation and subsequent resolubilization of calmodulin in a fashion whose biphasic dose-dependence paralleled that seen for its action in promoting calmodulin's phosphorylation. NaCl attenuated, in apparently identical dose-dependent fashions, poly-L-lysine's ability to both elicit the precipitation of calmodulin and to promote its phosphorylation. The presence of added Ca2+ led to a small potentiation of poly-L-lysine-dependent calmodulin phosphorylation at low concentrations, with inhibition occurring at higher concentrations where Ca2+ was shown to block calmodulin precipitation by poly-L-lysine. It is suggested that calmodulin can be phosphorylated by the insulin receptor only when it is cross-linked in a multivalent fashion to a suitable polybasic substance so that it forms large multimeric aggregates. Such a requirement for the formation of an aggregate between calmodulin and a suitable polybasic species may place specific constraints on the ability of calmodulin to serve as a substrate for receptor tyrosyl kinases within the cell.

Calmodulin expression during proliferative activation of human T lymphocytes

We have investigated the levels of calmodulin mRNA species and calmodulin protein during proliferation of human T lymphocytes. Quiescent lymphocytes expressed the 1.7 kb transcript of CaM I, the 1.4 kb of CaM II and the 2.3 kb of CaM III. Phytohaemagglutinin added to peripheral blood lymphocytes induced DNA replication which started at 48 h and reached a maximum at 72 h after activation. All the species of calmodulin mRNAs, including the 4.0 kb transcript of CaM I and the 0.8 kb of CaM III which were not detected in quiescent cells, increased during lymphocyte proliferation. At 72 h after activation, the increase of CaM I and CaM II transcripts were found to be 2-fold whereas CaM III mRNAs increased 9-fold. The cellular content of calmodulin protein was also found to increase during proliferation and calmodulin accumulations in cytosol and nuclei of activated cells were observed. Two calmodulin binding proteins of 180 and 170 kD were found to increase in the nuclei of proliferating lymphocytes, whereas on the contrary 3 other calmodulin binding proteins of 110, 62 and 60 kD decreased during proliferation.

Localization of the multiple calmodulin messenger RNAs in differentiated PC12 cells

Calmodulin, a ubiquitous calcium-binding protein which is involved in many biological processes, including cell proliferation and differentiation, has been shown to be encoded by three genes from which five calmodulin messenger RNAs are transcribed. In our previous studies, using the PC12 pheochromocytoma cell line as a model system for neuronal differentiation, all five calmodulin messenger RNAs were found to be present, and treatment with both nerve growth factor and dibutyryl cyclic AMP, which induce neurite outgrowth in these cells, increased the level of calmodulin and differentially increased the levels of the various calmodulin messenger RNAs. In an attempt to uncover the nature of the differential increase in the calmodulin messenger RNAs during neuronal differentiation, we examined here the subcellular distribution of the individual calmodulin messenger RNAs in PC12 cells treated with nerve growth factor and dibutyryl cyclic AMP by in situ hybridization cytochemistry, using radiolabeled oligodeoxynucleotide probes. Using an oligodeoxynucleotide probe which detects all of the calmodulin transcripts, the calmodulin messenger RNAs were found to be distributed throughout the cell bodies of differentiated PC12 cells; significant amounts of calmodulin messenger RNAs were also found in most neurites (approximately 70% of the total number). Using specific probes for the calmodulin messenger RNAs derived from each calmodulin gene, distinct patterns of localization of the different calmodulin messenger RNAs were revealed. The messenger RNAs from calmodulin genes I and II were readily detected in all cell bodies and in about one-half of the neurites. In contrast, a weak signal for the messenger RNAs from calmodulin gene III was associated with cell bodies, while no significant signal was found in neurites. A population distribution analysis of the labeling of individual PC12 cell bodies, as determined by counting autoradiographic grains, revealed differences in the relative abundance of each group of messenger RNAs derived from each of the three calmodulin genes. The order of relative abundance of the messenger RNAs in cell bodies was found to be: calmodulin gene II messenger RNA > calmodulin gene I messenger RNAs >> calmodulin gene III messenger RNAs. An analysis of the labeling density along neurites indicated a similar density of neuritic messenger RNAs from calmodulin gene I and calmodulin gene II, whereas there was no significant signal for the messenger RNAs from calmodulin gene III.(ABSTRACT TRUNCATED AT 400 WORDS)

Reversible effect of calcium-binding protein regucalcin on the Ca(2+)-induced inhibition of deoxyuridine 5'-triphosphatase activity in rat liver cytosol

The effect of regucalcin, a calcium-binding protein isolated from rat liver cytosol, on deoxyuridine 5'-triphosphatase (dUTPase) in the cytosol of rat liver was investigated. Addition of Ca2+ up to 5.0 microM to the enzyme reaction mixture caused a significant decrease of dUTPase activity, while Zn2+, Cd2+, Co2+, Al3+, Mn2+ and Ni2+ (10 microM) did not have an appreciable effect. The Ca(2+)-induced decrease of dUTPase activity was reversed by the presence of regucalcin; the effect was complete at 1.0 microM of the protein. Regucalcin had no effect on the basal activity of the enzyme. Meanwhile, the reversible effect of regucalcin on the Ca2+ (10 microM)-induced decrease of dUTPase activity was not altered by the coexistence of Cd2+ or Zn2+ (10 microM). The present data suggest that liver cytosolic dUTPase is uniquely regulated by Ca2+ of various metals, and that the Ca2+ effect is reversed by regucalcin.

Association of calmodulin with isolated nuclei from rat hepatocytes

Calmodulin plays an important role in regulating cell proliferation and intranuclear processes (J. Biol. Chem. 265: 18595, 1990). Therefore we studied the association of 125I-calmodulin with highly purified rat hepatocyte nuclear preparations which were characterized by marker enzymes and electron microscopy. Steady-state association of 125I-calmodulin was reached within 5 minutes. Half-maximal binding was achieved at approximately 7.1 microM. This association was partially Ca(2+)-dependent, but was not influenced by ATP, GTP or wheat germ agglutinin. Ultrastructural autoradiography showed specific association of 125I-calmodulin with peripheral and non-peripheral heterochromatin, nuclear membranes, and nucleoli. Specific binding (ratio of the grain density of 125I-calmodulin to Na125I) was greatest in the regions of the nucleoli and non-peripheral heterochromatin. The data indicate that exogenous calmodulin can associate with specific nuclear components in an energy-independent and Ca(2+)-dependent manner.