Differential activity of cathepsin L in human placenta at two different stages of gestation

Expression and Regulation of a Novel Decidual Cells-Derived Estrogen Target during Decidualization

During decidualization in rodents, uterine stromal cells undergo extensive reprogramming to differentiate into distinct cell types, forming primary decidual zones (PDZs), secondary decidual zones (SDZs), and layers of undifferentiated stromal cells. The formation of secondary decidual zones is accompanied by extensive angiogenesis. During early pregnancy, besides ovarian estrogen, de novo synthesis of estrogen in the uterus is essential for the progress of decidualization. However, the molecular mechanisms are not fully understood. Studies have shown that Cystatin B (Cstb) is highly expressed in the decidual tissue of the uterus, but the regulation and mechanism of Cstb in the process of decidualization have not been reported. Our results showed that Cstb was highly expressed in mouse decidua and artificially induced deciduoma via in situ hybridization and immunofluorescence. Estrogen stimulates the expression of Cstb through the Estrogen receptor (ER)α. Moreover, in situ synthesis of estrogen in the uterus during decidualization regulates the expression of Cstb. Silencing the expression of Cstb affects the migration ability of stromal cells. Knockdown Cstb by siRNA significantly inhibits the expression of Dtprp, a marker for mouse decidualization. Our study identifies a novel estrogen target, Cstb, during decidualization and reveals that Cstb may play a pivotal role in angiogenesis during mouse decidualization via the Angptl7.

Cysteine Cathepsins and Their Prognostic and Therapeutic Relevance in Leukemia

Cysteine cathepsins are lysosomal proteases that require Cys-His ion pair in their catalytic site for enzymatic activity. While their aberrant expression and oncogenic functions have been widely reported in solid tumors, recent findings suggest that these proteases also play an important role in the pathogenesis of hematological malignancies. In this review, we summarize the potential clinical implications of cysteine cathepsins as diagnostic and prognostic markers in leukemia, and present evidences which supports the utility of these proteases as potential therapeutic targets in hematological malignancies. We also highlight the available information on the expression patterns, regulation, and potential functions of cysteine cathepsins in normal hematopoiesis and hematological malignancies. In hematopoiesis, cysteine cathepsins play a variety of physiological roles including regulation of hematopoietic stem cell adhesion in the bone marrow, trafficking, and maturation. They are also involved in several functions of immune cells which include the selection of lymphocytes in the thymus, antigen processing, and presentation. However, the expression of cysteine cathepsins is dysregulated in hematological malignancies where they have been shown to play diverse functions. Interestingly, several pieces of evidence over the past few years have demonstrated overexpression of cathepsins in leukemia and their association with worst survival outcomes in patients. Strategies aimed at altering the expression, activity, and subcellular localization of these cathepsins are emerging as potential therapeutic modalaties in the management of hematological malignancies. Recent findings also suggest the involvement of these proteases in modulating the immune response in leukemia and lymphomas.

Involvement of a host Cathepsin L in symbiont-induced cell death

The cathepsin L gene of the host squid, Euprymna scolopes, is upregulated during the first hours of colonization by the symbiont Vibrio fischeri. At this time, the symbiotic organ begins cell death-mediated morphogenesis in tissues functional only at the onset of symbiosis. The goal of this study was to determine whether Cathepsin L, a cysteine protease associated with apoptosis in other animals, plays a critical role in symbiont-induced cell death in the host squid. Sequence analysis and biochemical characterization demonstrated that the protein has key residues and domains essential for Cathepsin L function and that it is active within the pH range typical of these proteases. With in situ hybridization and immunocytochemistry, we localized the transcript and protein, respectively, to cells interacting with V. fischeri. Activity of the protein occurred along the path of symbiont colonization. A specific Cathepsin L, nonspecific cysteine protease, and caspase inhibitor each independently attenuated activity and cell death to varying degrees. In addition, a specific antibody decreased cell death by ~50%. Together these data provide evidence that Cathepsin L is a critical component in the symbiont-induced cell death that transforms the host tissues from a colonization morphology to one that promotes the mature association.

Pre-eclampsia has an adverse impact on maternal and fetal health

Pre-eclampsia (preE) is a multifaceted complication found uniquely in the pregnant patient and one that has puzzled scientists for years. PreE is not a single disorder, but a complex syndrome that is produced by various pathophysiological triggers and mechanisms affecting about 5% of obstetrical patients. PreE is a major cause of premature delivery and maternal and fetal morbidity and mortality. PreE is characterized by de novo development of hypertension and proteinuria after 20 weeks of gestation and affects nearly every organ system, with the most severe consequences being eclampsia, pulmonary edema, intrauterine growth restriction, and thrombocytopenia. PreE alters the intrauterine environment by modulating the pattern of hormonal signals and activating the detrimental cellular signaling that has been transported to the fetus. The fetus has to adapt to this intrauterine environment with detrimental signals. The adaptive changes increase the risk of disease later in life. This review defines the predisposition and causes of preE and the cellular signaling detrimental to maternal health during preE. Moreover, the risk factors for diseases that are transmitted to the offspring have been addressed in this review. The detrimental signaling molecules that have been overexpressed in preE patients raises the possibility that those signals could be therapeutically blocked one day.

Integral proteomic analysis of blastocysts reveals key molecular machinery governing embryonic diapause and reactivation for implantation in mice

Among nearly 100 mammalian species, implantation can be suspended at blastocyst stage for a certain time and reactivated under favorable conditions, a phenomenon known as embryonic diapause. Until now, the underlying molecular mechanism governing embryonic diapause and reactivation for implantation remained largely unknown. Here we conducted the first integral proteomic analysis of blastocysts from diapause to reactivation by using a physiologically relevant mouse delayed implantation model. More than 6000 dormant and reactivated blastocysts were used for the proteomic analysis. A total of 2255 proteins were detected. Various cellular and molecular processes, including protein translation, aerobic glycolysis, pentose phosphate pathway, purine nucleotide biosynthesis, glutathione metabolism, and chromatin organization were identified as differentially regulated. In particular, we demonstrated a remarkable activation of mitochondria in blastocysts upon reactivation from dormancy, highlighting their essential physiological significance. Moreover, the activities of the endosome-lysosome system were prominently enhanced in the mural trophectoderm of reactivated blastocysts, accompanied by active phagocytosis at the fetal-maternal interface, suggesting a critical role in promoting trophoblast invasion. Collectively, we provided an integral proteomic view upon the regulatory network of blastocyst reactivation from diapause, which will help to better interpret the nature of embryonic diapause and reactivation in wild animals and to identify molecular indicators for selecting blastocysts with high implantation competency.

The evolution of viviparity: molecular and genomic data from squamate reptiles advance understanding of live birth in amniotes

Squamate reptiles (lizards and snakes) are an ideal model system for testing hypotheses regarding the evolution of viviparity (live birth) in amniote vertebrates. Viviparity has evolved over 100 times in squamates, resulting in major changes in reproductive physiology. At a minimum, all viviparous squamates exhibit placentae formed by the appositions of maternal and embryonic tissues, which are homologous in origin with the tissues that form the placenta in therian mammals. These placentae facilitate adhesion of the conceptus to the uterus as well as exchange of oxygen, carbon dioxide, water, sodium, and calcium. However, most viviparous squamates continue to rely on yolk for nearly all of their organic nutrition. In contrast, some species, which rely on the placenta for at least a portion of organic nutrition, exhibit complex placental specializations associated with the transport of amino acids and fatty acids. Some viviparous squamates also exhibit reduced immunocompetence during pregnancy, which could be the result of immunosuppression to protect developing embryos. Recent molecular studies using both candidate-gene and next-generation sequencing approaches have suggested that at least some of the genes and gene families underlying these phenomena play similar roles in the uterus and placenta of viviparous mammals and squamates. Therefore, studies of the evolution of viviparity in squamates should inform hypotheses of the evolution of viviparity in all amniotes, including mammals.

Uterine gene expression in the live-bearing lizard, Chalcides ocellatus, reveals convergence of squamate reptile and mammalian pregnancy mechanisms

Although the morphological and physiological changes involved in pregnancy in live-bearing reptiles are well studied, the genetic mechanisms that underlie these changes are not known. We used the viviparous African Ocellated Skink, Chalcides ocellatus, as a model to identify a near complete gene expression profile associated with pregnancy using RNA-Seq analyses of uterine transcriptomes. Pregnancy in C. ocellatus is associated with upregulation of uterine genes involved with metabolism, cell proliferation and death, and cellular transport. Moreover, there are clear parallels between the genetic processes associated with pregnancy in mammals and Chalcides in expression of genes related to tissue remodeling, angiogenesis, immune system regulation, and nutrient provisioning to the embryo. In particular, the pregnant uterine transcriptome is dominated by expression of proteolytic enzymes that we speculate are involved both with remodeling the chorioallantoic placenta and histotrophy in the omphaloplacenta. Elements of the maternal innate immune system are downregulated in the pregnant uterus, indicating a potential mechanism to avoid rejection of the embryo. We found a downregulation of major histocompatability complex loci and estrogen and progesterone receptors in the pregnant uterus. This pattern is similar to mammals but cannot be explained by the mammalian model. The latter finding provides evidence that pregnancy is controlled by different endocrinological mechanisms in mammals and reptiles. Finally, 88% of the identified genes are expressed in both the pregnant and the nonpregnant uterus, and thus, morphological and physiological changes associated with C. ocellatus pregnancy are likely a result of regulation of genes continually expressed in the uterus rather than the initiation of expression of unique genes.

Epigenetic regulation of cathepsin L expression in chronic myeloid leukaemia

The expression and significance of cathepsin L (CTSL) has been extensively studied in solid tumours. However no such information in chronic myeloid leukaemia (CML) was available. We investigated the activity and expression of this protease in peripheral blood mononuclear cells (PBMCs) of 47 adult CML patients. Thirty adults suffering from systemic diseases and 50 healthy volunteers served as controls. The mRNA levels of CTSL, its specific endogenous inhibitor cystatin C and transcriptional up-regulator vascular endothelial growth factor (VEGF) were quantitated by real-time qPCR. CTSL protease activity and its mRNA expression were significantly higher in CML chronic phase (CP) patients compared to CML accelerated phase/blast crisis (AP/BC) patients and controls (P≤ 0.001). VEGF whose expression was most pronounced in CP and declined (P≤ 0.001) in the advanced phases of the malignancy exhibited a strong positive correlation with CTSL expression (r= 0.97; P≤ 0.001). Cystatin C expression was significantly lower (P≤ 0.001) in CML and displayed inverse correlation with CTSL (r=−0.713; P≤ 0.001) activity. CTSL promoter was significantly hypomethylated in CML CP compared to CML AP/BC patients as well as controls. K562, a BC CML cell line displayed CTSL activity, expression and methylation status of CTSL promoter that was comparable to CML AP/BC patients. Treatment of these cells or PBMCs isolated from CML AP/BC patients with 5′-aza-cytidine resulted in a dramatic increase in CSTL activity and/or expression thereby demonstrating the role of promoter methylation in the stage specific expression of CTSL in CML. Differential expression of CTSL in CML at various stages of malignancy may prove useful in identification of the high-risk patients thereby facilitating better management of disease.

Cathepsins B and L in peripheral blood mononuclear cells of pediatric acute myeloid leukemia: potential poor prognostic markers

The diagnostic and prognostic significance of cathepsin B (CTSB) and L (CTSL) is well documented for solid tumors. However, their significance in acute leukemias is lacking. This study was planned to investigate expression and significance of these proteases in peripheral blood mononuclear cells (PBMCs) of patients with pediatric acute myeloid leukemia (AML). CTSL and CTSB activities were assayed in PBMCs of 24 children with AML and ten healthy controls by spectrofluorimetry. The mRNA levels of these proteases and their specific endogenous inhibitor cystatin C and transcriptional upregulator vascular endothelial growth factor (VEGF) were quantitated by real-time PCR. Correlation analysis of CTSL and CTSB activities/expression with their inhibitor/upregulator and event-free survival (EFS) was done using appropriate statistical tools. CTSL and CTSB protease activity and their mRNA expression were significantly higher in AML patients compared to controls (p ≤ 0.001). A strong positive correlation was observed between VEGF expression and CTSL (r = 0.812; p ≤ 0.001). Similarly, VEGF exhibited a strong positive correlation with CTSB (r = 0.501; p = 0.013). Cystatin expression though significantly high (p ≤ 0.001) in AML was negatively correlated with CTSL (r = -0.920; p ≤ 0.001) and CTSB (r = -0.580, p ≤ 0.001) expression. AML patients with higher CTSL and CTSB activity exhibited an inferior EFS (CTSL: p = 0.045; CTSB: p = 0.002) and overall survival (OS; CTSL: p = 0.05; CTSB: p = 0.004) compared to patients with lower levels of these proteases. This is the first report demonstrating increased expression of CTSL and CTSB in AML, mechanism of their increased expression in relation to VEGF, and their association with poor EFS and OS. These results suggest a potential utility of these proteases as prognostic markers for this malignancy.

Proteomic analyses associate cystatin B with restricted HIV-1 replication in placental macrophages

Mononuclear phagocytes (MP; monocytes, tissue macrophages, and dendritic cells) are reservoirs, vehicles of dissemination, and targets for persistent HIV infection. However, not all MP population equally support viral growth. Such differential replication is typified by the greater ability of placental macrophages (PM), as compared to blood borne monocyte-derived macrophages (MDM), to restrict viral replication. Since cytosolic protein patterns can differentiate macrophage subtypes, we used a proteomics approach consisting of surface-enhanced laser desorption ionization time-of-flight (SELDI-TOF), tandem mass spectrometry, and Western blots to identify differences between the uninfected and HIV-infected PM and MDM protein profiles linked to viral growth. We performed proteome analysis of PM in the molecular range of 5-20kDa. We found that a SELDI-TOF protein peak with an m/z of 11,100, which was significantly lower in uninfected and HIV-infected PM than in MDM, was identified as cystatin B (CSTB). Studies of siRNA against CSTB treatment in MDM associated its expression with HIV replication. These data demonstrate that the low molecular weight placental macrophage cytosolic proteins are differentially expressed in HIV-infected PM and MDM and identify a potential role for CSTB in HIV replication. This work also serves to elucidate a mechanism by which the placenta protects the fetus from HIV transmission.

Transcriptional upregulation of human cathepsin L by VEGF in glioblastoma cells

The role of vascular endothelial growth factor (VEGF) on cathepsin L expression was investigated in human glioblastoma cells (U87MG). Our results demonstrate the transcriptional upregulation of cathepsin L expression by VEGF. Transient transfection of U87MG cells with VEGF expression vector significantly increased cathepsin L activity. These results were further corroborated by a parallel increase in the mRNA levels and promoter activity of cathepsin L by VEGF. By deletion analysis, we identified a 47 base pair VEGF response element (VRE) in human cathepsin L promoter. Site directed mutagenesis studies demonstrated that both SP-1 and AP-4 motifs present in this region contribute to VEGF responsiveness. These results prove for the first time that over-expression of VEGF in human glioblastoma cells induces cathepsin L expression at the transcriptional level. This mechanism could be involved in the enhanced tumorogenic potential of these cells.

Increased cystatin C expression in the pre-eclamptic placenta

Trophoblast invasion is regulated by proteinases and their inhibitors. Cystatin C inhibits cysteine proteinases. The serum concentration of cystatin C is increased in late pregnancy and pre-eclampsia. We aimed to investigate whether the expression of cystatin C is increased in the pre-eclamptic placenta and to investigate the expression pattern of cystatin C mRNA and protein in placental tissue. Tissue samples from the central part of the placenta from 13 normal and 22 pre-eclamptic pregnancies were included. We used real-time polymerase chain reaction (RT-PCR) and in situ hybridization for mRNA expression analysis and immunohistochemistry and Western blotting for protein expression analysis. RT-PCR showed a significantly higher expression of cystatin C mRNA in pre-eclampsia than in normal pregnancy, with the highest expression in cases with severe pre-eclampsia. In situ hybridization revealed a distinct pattern of high expression in the extravillous trophoblast cells of the basal plate and low expression in the syncytiotrophoblast covering villi. The cystatin C protein distribution matched the mRNA expression pattern. Western blot analysis revealed an increased protein expression in cases with severe pre-eclampsia and confirmed the presence of cystatin C in amniotic fluid samples. The high expression of cystatin C mRNA in the extravillous trophoblast cells of the basal plate suggests a role for cystatin C in the regulation of proteases in placentation. Placental expression and secretion of cystatin C could contribute to the elevated maternal plasma levels seen in pre-eclampsia.

The importance of cysteine cathepsin proteases for placental development

The typically lysosomal family of cysteine cathepsin proteases has been implicated in the development of the placenta in particular, from studies in the mouse. Here, we analysed overall expression, regulation and presence of transcript isoforms of cysteine cathepsins during human extra-embryonic development. All 11 family members are expressed in human placental tissues, and many are differentially regulated during gestation. Several cysteine cathepsins exhibit deregulated expression levels in placentas from pregnancies complicated by pre-eclampsia. The localization of cathepsin B predominantly in placental and decidual macrophages suggests a role in the physiological functions of these cells in mediating villous angiogenesis and decidual apoptosis. Cathepsin L levels are highest in a subpopulation of invasive cytotrophoblasts. Reflecting the expression pattern of two murine cathepsins, these data give insights into the evolutionary conservation of cathepsin function that is not necessarily exhibited by gene pairs defined by highest sequence similarity. Furthermore, cathepsin L protein localization in uterine epithelial cells demonstrates the in vivo occurrence of intranuclear cathepsin L isoforms. The zonally restricted expression of cathepsin in the syncytiotrophoblast may be important for the metabolic breakdown of maternal nutrients. Overall, the distribution and abnormal expression levels in pre-eclamptic placentas indicate that cysteine cathepsins may play important roles during normal placentation and in the etiology of pre-eclampsia.

Involvement of MAPK pathway in TNF- -induced MMP-9 expression in human trophoblastic cells

The aim of this article was to investigate the signalling pathways involved in metalloproteinase-9 (MMP-9) expression induced by tumour necrosis factor-alpha (TNF-alpha) in first-trimester trophoblastic cells. TNF-alpha-induced MMP-9 expression, secretion and activity were completely blocked by stress-activated protein kinase/jun kinase (SAPK/JNK) and Erk inhibitors (SP600 125 and U0126 respectively) but not by p38 mitogen-activated protein kinase (MAPK) inhibitors (SB203 580 and SB202 190). Stimulation of HIPEC 65 cells with TNF-alpha caused phosphorylation of JNK and extracellular signal-regulated kinase 1/2 (Erk1/2), with a peak after 20 min of treatment. Transcription factors nuclear factor-kappaB (NF-kappaB) and activator protein 1 (AP-1)-binding site were identified as the cis-elements involved in TNF-alpha activation as determined by electromobility shift assays. TNF-alpha-induced transactivation of NF-kappaB was inhibited by U0126, whereas TNF-alpha-induced transactivation of AP-1 was inhibited by SP600 125. Taken together, these results indicate that in trophoblastic cells, TNF-alpha probably activates two different pathways leading to MMP-9 expression: (a) Erk1/2 pathway which in turn initiates NF-kappaB activation and (b) SAPK/JNK pathway that activates AP-1.

Role of cathepsins and cystatins in patients with recurrent miscarriage

In the implantation, trophoblasts penetrate maternal decidua by secreting proteases. It has been reported that cathepsins are highly expressed in the mouse villi, and play an important role in normal embryonal growth and decidualization. In this study, we evaluated cathepsins and their endogenous inhibitors, cystatins, in tissue and serum of patients with recurrent miscarriage. Decidua and villi were surgically collected from 22 patients and 12 healthy women. Immunohistochemistry was performed with antibodies against cathepsins, stefin A (cystatin A), stefin B (cystatin B) and cystatin C. The concentrations of cathepsins, stefins and cystatin C were measured by Enzyme-linked immunosorbent assay. In addition, we measured the serum level of cystatin C in 85 Japanese women with recurrent miscarriage. Staining of cathepsin B, D, H, L, stefin B and cystatin C was observed in the cytoplasm of epithelial cells in decidua. Stefin A was expressed on the surface of the trophoblast. The concentration of cathepsin B and H in patients' decidua was significantly higher than in control individuals. The serum level of cystatin C was significantly lower in patients than in control individuals. Our findings suggest that the regulation of the cathepsin-cystatin system may play an important role in patients with recurrent miscarriage.

Comparison of expression of cathepsins B and L and MMP2 in endothelial cells and in capillary sprouting in collagen gel

The lysosomal cysteine proteinases cathepsins B and L are known to play an important role in the invasive growth of tumor cells, but their association with angiogenesis has been less well studied. The aim of this study was to determine the possible role of endothelial cell-associated cathepsins B and L in induced capillary growth in the aorta ring model of angiogenesis. Specific inhibitors of cysteine proteinases did not inhibit capillary growth in aorta ring culture and only slightly inhibited the degradation of surrounding collagen. In contrast, strong inhibition of both processes by the matrix metalloproteinase inhibitor BB-94 was observed, indicating the importance of endogenous MMP production in angiogenesis. In support of this finding, we demonstrated a significant increase in endogenous endothelial mRNA of MMP2, but not of cathepsins B and L, in proliferating primary human dermal microvascular endothelial cells (HMVEC-d) in culture. However, MMP2 mRNA expression was increased only when the cells were embedded in collagen but not when they were grown on plastic, regardless of the addition of the growth factors VEGF or bFGF. Moreover, on plastic the impairment of MMP2 induction by growth factors was observed. The differential effect of growth factors implies the crosstalk with integrin signaling as a consequence of binding to the different matrix. This study suggests that endothelial cell-associated cathepsins B and L are not involved in the invasive growth of capillaries from existing blood vessels and that the presence of collagen is necessary for MMP2 expression in endothelial cells.

Independent Downstream Gene Expression Profiles in the Presence of Estrogen Receptor α or β1

The two known forms of estrogen receptor (ER), alpha and beta, exhibit differences in structure, affinity for certain ligands, and tissue distribution, suggesting differential roles. It is of interest from several perspectives to determine whether the two receptors elicit similar or differing responses within the same cell type in the presence of the same ligand. To evaluate roles of ER, we have examined responses to estrogen in a rat embryonic fibroblast cell line model, normally naive to ER, engineered to stably express ERalpha or ERbeta. Rat1+ERalpha, Rat1+ERbeta, and precursor Rat1 cell lines were treated with estradiol-17beta (E(2); 1 nM) or an ethanol vehicle for 24 h. Total RNA was extracted, and cDNA generated and subjected to suppression subtractive hybridization (SSH), followed by differential screening using dot blot hybridization. In the presence of ERalpha, products were identified that represent classic responses to E(2), including markers for cell proliferation. In the presence of ERbeta, an alternate transcription profile was observed, including upregulation of pro-alpha-2(I) collagen. These data support a model in which ERalpha and ERbeta regulate unique subsets of downstream genes within a given cell type.

Identification of expressed sequence tags preferentially expressed in human placentas by in silico subtraction

OBJECTIVES

To identify expressed sequence tag (EST) clusters preferentially expressed in placentas.

METHODS

The National Center for Biotechnology's online UniGene database contains 14 placenta libraries. In silico (computer-based) subtraction compared placenta libraries against the remaining libraries to identify transcripts preferentially expressed in placentas. For known genes, placental expression or their use in prenatal diagnosis was then explored online using LocusLink and PubMed.

RESULTS

Placentas preferentially expressed 475 EST clusters. Of these, 18 EST clusters with no known function were expressed exclusively in placentas. Of the remaining 457 EST clusters, 90 showed preferential placental expression by >/=25 times. Of these 90, literature searches on the 45 EST clusters with known functions showed 44 linked to placental physiology or proposed as markers for prenatal diagnosis [i.e. beta-hCG, pregnancy-specific glycoproteins, human placental lactogens, pregnancy-associated plasma protein A (PAPP-A)]. Selected genes with known function in pregnancy but whose preferential placental expression fell below the factor of 25 threshold were also identified.

CONCLUSION

In silico subtraction identified 44 previously studied genes involved in placental physiology as well as 63 EST clusters preferentially expressed in placental tissue, which may serve as targets for future studies seeking novel markers for prenatal diagnosis or to better understand placental genetics.

Identification and characterization of a novel human cathepsin L splice variant

Human cathepsin L (hCATL) has been implicated in a variety of physiological and pathological processes. It was hitherto known to be encoded by four mRNA species, namely hCATL A, AI, AII and hCATL B, differing in their 5' untranslated regions (UTRs). Of these, hCATL A, AI and AII are produced by the alternative splicing of the same primary transcript. HCATL AI and hCATL AII, lack 27 and 90 bases, respectively, from the 3' end of exon 1 of hCATL A. The present study describes the identification of a new splice variant hCATL AIII, which similarly lacks 145 bases from the 3' end of exon 1 of hCATL A. It is produced by the splicing out of 136-280 bases of the first exon in addition to intron 1 of hCATL A, which together serve as an intron for hCATL AIII. HCATL AIII was observed to be the most abundant splice variant in five different human cell lines. In vitro transcription coupled translation studies revealed that hCATL AIII is translated with 4.4-, 3.9- and 1.6-fold higher efficiency as compared to hCATL A, AI and AII, respectively. These results were further confirmed by measuring the enzymatic activities of the in vitro translated products. Cloning of hCATL AIII UTR upstream to luciferase reporter gene resulted in a 3.75-fold higher expression of the reporter gene as compared to the luciferase construct containing UTR of hCATL A. Thus, we have identified a novel human cathepsin L splice variant, hCATL AIII, which is most abundant in human cell lines and is translated with highest efficiency. Our results demonstrate either the presence of a positive or absence of a negative cis-acting regulatory element(s) in the UTR of hCATL AIII that is sufficient to confer translational advantage to a heterologous mRNA. The predominance of this most efficiently translated splice variant in malignant cells suggests that it plays a key role in the over-expression of human cathepsin L in cancer.