Stromal morphological changes and immunophenotypic features of precancerous lesions and hepatocellular carcinoma.

AIMS: To evaluate stromal histopathological features and immunostaining expression for differential diagnosis of low- and high-grade dysplastic nodules (HGDN) to early and progressed hepatocellular carcinomas (eHCC, pHCC). MATERIALS: We evaluated sinusoid capillarisation (SC), solitary artery (SA), ductular reaction (DR), stromal invasion and expression of six biomarkers (GPC3, HSP70, GS, CD34, CK19, EpCAM) in a series of 97 cases. RESULTS: Stromal morphological changes, including SC, DR and SA, exhibited significant differences in differential diagnosis. In one indicator, SC had the best sensitivity (90.00%) and accuracy (85.42%), and SA had the best specificity at 88.89 %. In combinations, SC +and SA +were favourable and optimal. The immunoreactivity of GPC3, HSP70 and GS increased significantly in line with the stepwise progression of hepatocarcinogenesis. CONCLUSIONS: Stromal histopathology features are useful for diagnosing HGDN, eHCC and small HCC. The immunostaining panel of GPC3, HSP70 and GS can also be supplementary.

Identification of ampullary carcinoma mixed subtype using a panel of six antibodies and its clinical significance.

OBJECTIVES: To investigate the function of immunomarkers CK7, CK20, CK17, CDX2, MUC1, and MUC2 in the identification of primary ampullary carcinoma mixed subtype. METHODS: Forty-two cases of primary ampullary carcinoma were performed by immunohistochemical studies. The correlation between the mixed subtype and the other two subtypes and patient survival data was analyzed using the SPSS 16.0 statistical software. RESULTS: Among 42 cases, 12 (28.6%) cases were classified as mixed subtype, which showed variable expression patterns: 91.7% (11/12) for CK7, 83.3% (10/12) for CK20; 66.7% (8/12) for CK17, CDX2, and MUC1; and 50% (6/12) for MUC2. Ten (83.3%) mixed types coexpressed four or more immunomarkers. Eight (19%) intestinal subtypes mainly showed a positive expression of CK20, CDX2, and MUC2. Twenty-two (52.4%) pancreaticobiliary subtypes showed a positive expression of CK7, MUC1, and CK17. Stages III and IV diseases in mixed subtype (25%) and intestinal subtype (25%) were less than pancreaticobiliary subtype(63.6%) (p = 0.039). Follow-up data appeared to show a better survival rate for patients with mixed subtype than those with pancreaticobiliary subtypes. CONCLUSION: Immunohistochemical staining provided a more reliable means of diagnosing mixed ampulla carcinoma. Accurate subtyping of ampullary carcinoma is clinically important to select effective chemotherapy regimens and to assess disease prognosis.

Clinicopathological features and differential diagnosis of hepatocellular carcinoma in extrahepatic metastases.

Extrahepatic metastasis of hepatocellular carcinoma (HCC) may cause a diagnostic problem. All 195 cases of histologic and immunostained sections were reviewed retrospectively in one center. The expression of arginase-1 (Arg-1), hepatocyte paraffin-1 (HepPar-1), glypican-3 (GPC-3), and α-Fetoprotein (AFP) was evaluated. Eighty cases of metastatic tumors of the liver were also collected to verify their effectiveness. Totally 151 cases had previous history of HCC, in whom 49 had history of liver transplantation. Forty-four cases were diagnosed as metastatic HCC at initial presentation. The most common extrahepatic metastatic sites were bone (57%), followed by lung, lymph node, etc. Around 19 cases were positive for 1 marker, 22 were positive for 2 markers, 95 were positive for 3 markers, and 59 were positive for 4 markers. With the number of antibody increased in the panel, the negative cases decreased. The sensitivity of ARG, GPC-3, HepPar-1, and AFP was 82.6%, 89.2%, 83.6% and 53.8%, and the specificity was 98.3%, 94.8%, 96.2% and 100%, respectively. These data suggest that the panel of ARG-1, GPC-3, HepPar-1 and AFP has a high sensitivity and specificity to differentiate HCC from non-HCC. This study indicated that HCC should be considered when diagnosing metastasis of unclear origin. It is recommended to use the panel of ARG-1, GPC-3, HepPar-1 and AFP to differentiate HCC from non-HCC in extrahepatic metastasis, because of their sensitivity and specificity, especially in poorly differentiated lesions.

New tumour antigen PLAC1/CP1, a potentially useful prognostic marker and immunotherapy target for gastric adenocarcinoma.

AIM: To evaluate protein expression and clinical significance of PLAC1/CP1 antigen in primary gastric adenocarcinoma. METHODS: Protein expression of PLAC1/CP1 was analysed by tissue chip and immunohistochemistry in surgical specimens obtained from 119 patients with gastric cancer. The data were analysed using SPSS V.16.0 software applying the χ(2) test and Kaplan-Meier method. RESULTS: The positive expression frequency of PLAC1/CP1 protein was 61.3% (73/119 patients). The overall survival of patients with PLAC1/CP1 protein-positive expression was significantly lower than that of patients with PLAC1/CP1 protein-negative expression (p<0.05). There was no significant relationship between PLAC1/CP1 expression and patient gender, age, tumour position, tumour size, differentiation, gross type, lymph node or TNM stage. CONCLUSIONS: PLAC1/CP1 protein is expressed in over half of cases of primary gastric cancer, and PLAC1/CP1 protein expression is inversely correlated with patient survival. The data indicate that PLAC1/CP1 provides a marker for identifying gastric cancers with poor prognosis, and suggest that PLAC1/CP1 may provide a useful target for immunotherapy.

Identification of two new HLA-A*0201-restricted cytotoxic T lymphocyte epitopes from colorectal carcinoma-associated antigen PLAC1/CP1.

BACKGROUND: To explore the potential application of placenta-specific PLAC1/Cancer Placenta (CP) 1 antigen for immunotherapy in CRC patients, further identification of the cytotoxic T lymphocyte epitopes from this antigen is necessary. METHODS: We assessed the protein expression of PLAC1/CP1 using a tissue chip and immunochemistry staining in CRC samples. Simultaneously, we predicted four PLAC1/CP1-derived HLA-A*0201-restricted peptides by using reverse immunology methods. Peptide-specific CD8(+) T cell responses were assessed by an IFN-γ release ELISPOT assay. Effector CD8(+) T cells lyse HLA-A*0201 CRC cell line SW620 was detected in a granzyme-B release ELISPOT cytotoxicity assay. RESULTS: Our results indicated that PLAC1/CP1 was highly expressed in 56.7 % (55/97) of adenocarcinomas. PLAC1/CP1 protein expression was associated with CRC tumor differentiation, the tumor/node/metastasis stage, and lymph node metastasis. Two of four peptides showed high affinities in an HLA-A2 binding assay. In 66.7 % (6/9) of peripheral blood mononuclear cells of CRC samples with PLAC1/CP1 protein-positive expression, these two peptides, PLAC1/CP1 p41-50 (FMLNNDVCV) and PLAC1/CP1 p69-77 (HAYQFTYRV), were immunogenic in the induction of peptide-specific CD8(+) T cell responses as assessed by an IFN-γ release ELISPOT assay. Furthermore, the generated effector CD8(+) T cells could specifically lyse the PLAC1/CP1 HLA-A*0201 CRC cell line SW620 in a granzyme-B release ELISPOT cytotoxicity assay. CONCLUSIONS: These results show that the PLAC1/CP1 antigen is a possible prognostic marker of CRC and that PLAC1/CP1 p41-50 and PLAC1/CP1 p69-77 are novel HLA-A*0201-restricted CD8(+) T cell epitopes and potential targets for peptide-based immunotherapy in CRC patients.

Clinicopathologic spectrum and EBV status of post-transplant lymphoproliferative disorders after allogeneic hematopoietic stem cell transplantation.

Post-transplant lymphoproliferative disorders (PTLDs) are serious, life-threatening complications of solid-organ transplantation (SOT) and bone marrow transplantation, and are associated with high mortality. PTLDs represent a heterogeneous group of lymphoproliferative diseases, which show a spectrum of clinical, morphologic, and molecular genetic features ranging from reactive polyclonal lesions to frank lymphomas. We describe clinicopathologic features of 17 cases of PTLD after allogeneic hematopoietic stem cell transplantation (allo-HSCT), which were analyzed by in situ hybridization for EBV and a panel of antibodies directed against numerous antigens, including CD20, PAX5, CD3, bcl-6, CD10, MUM-1/IRF4, CD138, Kappa, Lambda, CD30, CD15, and Ki67. The cases included 13 males and 4 females with a median age of 31 years (range 9-49 years) and the PTLDs developed 1.5-19 months post-transplant (mean 4.7 months). The histological types indicated five cases of early lesions, two of plasmacytic hyperplasia and three of infectious mononucleosis-like PTLD. Eight cases were polymorphic PTLD, and four were monomorphic PTLD, including three of diffuse large B cell lymphoma, and one of plasmablastic lymphoma. Foci and sheets of necrosis were observed in five cases. The infected ratio of EBV was 88.2 %. Some cases were treated by reduction of immunosuppression, antiviral therapy, donor lymphocyte infusion, or anti-CD20 monoclonal rituximab. Eight cases died. The first half year after allo-HSCT is very important for the development of PTLD. The diagnosis of PTLD relies on morphology and immunohistochemistry, and EBV plays an important role in the pathogenesis of PTLD. The prognosis of PTLD is poor, and, notably, PTLD after allo-HSCT exhibits some features different from those of PTLD after SOT.

[Post-transplant lymphoproliferative disorder: a clinicopathologic study of 15 cases].

OBJECTIVE: To study the clinical and histopathologic features, diagnosis, pathogenesis and therapy of post-transplant lymphoproliferative disorders (PTLD). METHODS: The clinical and pathologic features of 15 cases of PTLD were retrospectively analyzed by light microscopy, immunohistochemistry and in-situ hybridization, according to the updated 2008 WHO classification of tumors of hematopoietic and lymphoid tissues. RESULTS: Amongst the 15 cases studied, 14 cases had received allogenic hematopoietic stem cell transplantation (AHSCT) and 1 case had received renal transplantation. There were altogether 12 males and 3 females. The male-to-female ratio was 4:1. The mean age was 30.4 years and the median age was 31 years (range from 9 to 60 years). PTLD developed 1.5 to 132 months after transplantation (median 13.0 months). The mean age of the 14 patients with AHSCT was 28.3 years (range from 9 to 45 years) and PTLD developed 1.5 to 19 months after transplantation (mean 4.5 months). Major clinical presentation included fever and lymphadenopathy. Twelve cases involved mainly lymph nodes and the remaining 3 cases involved tonsils, stomach and small intestine, respectively. The histologic types in 4 cases represented early lesions, including plasmacytic hyperplasia (n = 1) and infectious mononucleosis-like PTLD (n = 3). Seven cases were polymorphic PTLD, with 4 cases containing a predominance of large cells. Graft-versus-host disease was also seen in the case of small intestinal involvement. Four cases were monomorphic PTLD, 3 of which were diffuse large B-cell lymphoma, 1 was plasmablastic lymphoma and 1 was a mixture of monomorphic and polymorphic PTLD. Foci of necrosis were seen in 5 cases. The proliferating index of Ki-67 was high. The positive rate of EBV-encoded RNA in AHSCT was 92.9%. The duration of PTLD onset was shorter in EBV-positive cases (range from 1.5 to 7 months) than EBV-negative cases (range from 19 and 132 months). Some cases were treated by reduction of immunosuppression, antiviral agents or anti-CD20 monoclonal antibody Rituximab. The duration of follow-up in 14 patients ranged from 0 to 8 months. Five of the patients died of the disease. CONCLUSIONS: The diagnosis of PTLD relies on morphologic examination and immunohistochemistry. Most of them are of B-cell origin. EBV plays an important role in the pathogenesis of PTLD. The duration of disease onset is shorter in EBV-positive cases. PTLD in AHSCT cases occurs in younger age group, with shorter duration of onset, as compared to solid organ transplantation. The prognosis of PTLD is poor. The modalities of treatment include reduction of immunosuppression, antiviral agents or anti-CD20 monoclonal antibody Rituximab.

[Clinicopathologic study of 40 cases of mediastinal tumours of haematopoietic and lymphoid tissues].

OBJECTIVE: To study clinical and histopathological features, and diagnosis of mediastinal tumours of haematopoietic and lymphoid tissues (MTHL). METHODS: Forty cases of MTHL were analyzed for clinicopathology by microscopy and immunohistochemical staining and in situ hybridization, according to the updated 2008 WHO classification of tumours of haematopoietic and lymphoid tissues. RESULTS: In 40 cases of MTHL, there were 20 males and 20 females. The ratio of male/female was 1:1. The mean age was 31.8 years and median age was 29 years (range, 12 - 70 years).Superior vena cava syndrome was observed in 28 cases. The specimens of 4 cases were obtained by lumpectomy, whereas 36 cases by biopsy (25 cases by thoracoscopy, 1 by core needle aspiration). Twenty cases lay in anterior mediastinum, and 2 in posterior, 1 in superior, 8 in anterior and superior, 2 in posterior and superior, 2 in anterior and middle, 1 in middle and anterior mediastinum.Frozen section were performed in 28 cases, and 17 cases were diagnosed as tumours of haematopoietic and lymphoid tissues (consistency ratio was 60.7%). Twelve cases were classical Hodgkin lymphomas (cHL) (8 were nodular sclerosis subtype, and 3 were mixed cellarity, 1 was lymphocyte-rich subtype), and 10 were primary mediastinal (thymic) large B cell lymphoma (PMBCL), 10 were precursor lymphocyte neoplasm [8 were T lymphoblastic leukemia/lymphomas (T-LBL), 2 were B-LBL], 1 was MALT lymphoma, 1 was composite lymphoma (PMBCL and cHL), 2 were myeloid sarcomas, 4 were gray zone lymphomas (GZL) (3 had morphology reminiscent of cHL, and 1 of DLBCL, all cases were positive for CD20, PAX5, CD30 and CD15).EBER were detected in 11 cases by in situ hybridization, 2 of which were positive (18.2%), and the 2 positive cases were cHL. CONCLUSIONS: MTHLs occur predominantly in adolescents and young adults, mainly present as superior vena cava syndrome and anterior mediasinal masses. cHL, PMBCL, T-LBL were the most common MTHLs.GZLs mainly occur in young adults, those whose morphology reminiscent of cHL, immunohistochemistry reminiscent of PMBCL, and vice versa. Thoracoscopy, frozen section and a suitable panel of antibodies were practical approaches to MTHL.

[Morphologic changes of fallopian tubal epithelium in ovarian serous tumors].

OBJECTIVES: To study the morphologic changes of fallopian tubal epithelium in patients with ovarian serous epithelial tumors and to explore the relationship between the tubal epithelial changes and tumorigenesis of serous ovarian carcinoma. METHODS: The fallopian tubes in 79 cases of high-grade serous ovarian carcinoma, 12 cases of low-grade serous ovarian carcinoma, 16 cases of serous borderline ovarian tumor and 11 cases of non-ovarian benign tumors were serially examined under light microscope. Immunohistochemical study with EnVision method was used to detect the expression of p53 and bcl-2 protein in the fallopian tubal epithelium in all cases. The occurrences of secretory cell outgrowth (SCOUT), p53 signature, serous tubal intraepithelial carcinoma (STIC) and serous invasive carcinoma were analyzed. RESULTS: SCOUT in tubal epithelium was observed in 60.8% (48/79) of the high-grade serous carcinoma group, 4/12 of the low-grade serous carcinoma group, 3/16 of the serous borderline tumor group and 2/11 of the non-ovarian benign tumor group (P = 0.001). P53 signature, STIC and serous invasive carcinoma occurred only in the fallopian tubal epithelium of patients with high-grade serous ovarian carcinoma, with the positive rates being 29.1% (23/79), 15.2% (12/79) and 44.3% (35/79), respectively. Of the 23 cases with p53 signature, 17 cases had solitary lesion and 6 cases involved more than two sites. A total of 33 p53 signature positive foci were found, with 22 foci located at fimbria and 11 at ampulla. Bcl-2 expression was demonstrated in 90.9% of those foci (30/33). Of the 12 patients with STIC, 7 cases were solitary and 5 cases involved more than two sites. A total of 18 STIC foci were found, with 16 foci located at fimbria and 2 at ampulla. All of them were positive for bcl-2. CONCLUSIONS: SCOUT is found in fallopian tubal epithelium in patients with serous ovarian epithelial tumors, especially high-grade serious carcinoma. On the other hand, p53 signature, STIC and invasive serous carcinoma of tubal epithelium are observed only in patients with high-grade serous ovarian carcinoma, with a predilection of fimbrial involvement. Correlation exists between SCOUT, p53 signature, STIC and high-grade serous ovarian carcinomas. Bcl-2 and p53 immunostaining is helpful for demonstrating such lesions.

Epithelioid angiosarcoma of bone and soft tissue: a report of seven cases with emphasis on morphologic diversity, immunohistochemical features and clinical outcome.

AIMS AND BACKGROUND: Epithelioid angiosarcoma is a rare histopathologic variant of angiosarcoma characterized by an epithelioid morphology. This subset can histologically mimic non-vascular neoplasms and impose serious challenges in reaching a correct diagnosis, especially in the context of limited tissue sampling (e.g., needle core biopsy). To improve recognition of epithelioid angiosarcoma - and the spectrum of morphologic diversity associated with this rare variant - and to avoid a misdiagnosis, we describe the clinical, histopathologic, and immunohistochemical findings of cases of epithelioid angiosarcoma diagnosed at our institution. METHODS AND STUDY DESIGN: Seven cases of epithelioid angiosarcoma with appropriate pathologic material were identified from our archives. Immunohistochemistry was used to detect the expression of CD31, CD34, Factor VIII, cytokeratin, epithelial membrane antigen, vimentin, HMB45, CD1a, CD68, lysozyme, CD45, desmin, and smooth muscle actin in all cases. Follow-up information was obtained by reviewing medical records or by direct communication with family members. RESULTS: The lesions involved the bone (n = 4) and soft tissues (n = 3). Microscopically, all tumors had a predominantly diffuse growth pattern, with a focal nested architecture in 6 cases, which closely mimicked metastatic carcinoma. The initial biopsy was performed in 2 of 6 patients and revealed the presence of a malignant neoplasm suggestive of metastatic carcinoma. Immunohistochemically, the epithelioid endothelial cells usually showed strong reactivity for CD31 (7/7), variable or focal positive staining for CD34 (5/7), Factor VIII (4/7), cytokeratin (6/7), epithelial membrane antigen (2/7), vimentin (7/7), and CD68 (3/7). In contrast, they were negative for CD1a, HMB45, lysozyme, CD45, desmin, and smooth muscle actin. Three patients died of disease within one year of the diagnosis, 2 patients developed local recurrence or metastases, and another 2 were disease-free at this writing. CONCLUSIONS: With any unusual epithelioid neoplasm displaying some or all of the morphologic features described above, epithelioid angiosarcoma should be included in the differential diagnosis. In such an instance, endothelial markers should be incorporated in the immunohistochemical analysis to avoid misdiagnosis, particularly with limited sampling.

Phosphomimetic mutations enhance oligomerization of phospholemman and modulate its interaction with the Na/K-ATPase.

Na/K-ATPase (NKA) activity is dynamically regulated by an inhibitory interaction with a small transmembrane protein, phospholemman (PLM). Inhibition is relieved upon PLM phosphorylation. Phosphorylation may alter how PLM interacts with NKA and/or itself, but details of these interactions are unknown. To address this, we quantified FRET between PLM and its regulatory target NKA in live cells. Phosphorylation of PLM was mimicked by mutation S63E (PKC site), S68E (PKA/PKC site), or S63E/S68E. The dependence of FRET on protein expression in live cells yielded information about the structure and binding affinity of the PLM-NKA regulatory complex. PLM phosphomimetic mutations altered the quaternary structure of the regulatory complex and reduced the apparent affinity of the PLM-NKA interaction. The latter effect was likely due to increased oligomerization of PLM phosphomimetic mutants, as suggested by PLM-PLM FRET measurements. Distance constraints obtained by FRET suggest that phosphomimetic mutations slightly alter the oligomer quaternary conformation. Photon-counting histogram measurements revealed that the major PLM oligomeric species is a tetramer. We conclude that phosphorylation of PLM increases its oligomerization into tetramers, decreases its binding to NKA, and alters the structures of both the tetramer and NKA regulatory complex.

[Immunohistochemistry of p57 and p53 protein in differential diagnosis of hydropic abortion, partial and complete hydatidiform mole].

OBJECTIVE: To investigate the role of p57 and p53 immunohistochemistry in the differential diagnosis of hydropic abortion, partial hydatidiform mole and complete hydatidiform mole. METHODS: Immunohistochemical stains (EnVision method) for p57 and p53 were performed in tissue samples of normal placenta chorionic villi (n=10), abortion chorionic villi (n=12), partial hydatidiform (n=23) and complete hydatidiform moles (n=20). RESULTS: The expression of p57 was predominantly localized in the nuclei of villous cytotrophoblasts and stromal cells. The positive rates of p57 in normal placenta, hydropic abortion and partial hydatidiform mole were 10/10, 12/12, and 100% (23/23), respectively, with no significant difference among the groups (P>0.05). However, none of the complete hydatidiform moles analyzed exhibited p57 positivity in cytotrophoblasts and stromal cells. There was a significant difference between partial and complete hydatidiform moles (P<0.05). The expression of p53 was observed in the nuclei of cytotrophoblastic cells and intermediate trophoblasts. No p53 expression was seen in normal placenta and only 1 of 12 hydropic abortion showed p53 positivity. The positive rates of p53 expression in partial and complete hydatidiform mole were 60.9% (14/23) and 85.0% (17/20) respectively. It was significantly higher in partial hydatidiform mole than that in hydropic abortion. A significant difference was also found between partial and complete hydatidiform moles (P<0.05). CONCLUSIONS: Our findings confirm that p57 immunohistochemistry assists the differential diagnosis of complete hydatidiform mole from partial hydatidiform mole. Expression of p53 may be helpful in distinguishing partial hydatidiform mole from hydropic abortion.

[Expression of PLAC1/CP1 genes in primary colorectal carcinoma and its clinical significance].

OBJECTIVE: To study the expression and significance of PLAC1/CP1 genes in patients with primary colorectal carcinoma. METHODS: The expression of PLAC1/CP1 genes in 97 cases of colorectal carcinoma was studied using tissue chip technology and immunohistochemistry. RESULTS: The rate of PLAC1/CP1 proteins expression in the cases studied was 56.7% (55/97), with 27.8% (27/97) being nuclear staining and 43.3% (42/97) being cytoplasmic staining. The percentage of expression was higher in women than in men (χ(2) = 6.567, P = 0.010). The expression in poorly differentiated colorectal carcinoma was significantly higher than that in the well or moderately differentiated carcinoma (χ(2) = 8.321, P = 0.016). The expression was also significantly higher in stage TNM III or IV tumors than in stage TNM I or II tumors (χ(2) = 18.726, P = 0.000). The rate was higher in cases with lymph node metastasis than in those with negative lymph nodes (χ(2) = 17.407, P = 0.000), and was higher as the number of metastasis increasing (χ(2) = 22.632, P = 0.000). CONCLUSION: The expression of PLAC1/CP1 genes correlates with various clinical and pathologic parameters. It carries prognostic significance and may represent a potential target for immunotherapy.

Differential integration of Ca2+-calmodulin signal in intact ventricular myocytes at low and high affinity Ca2+-calmodulin targets.

Cardiac myocyte intracellular calcium varies beat-to-beat and calmodulin (CaM) transduces Ca2+ signals to regulate many cellular processes (e.g. via CaM targets such as CaM-dependent kinase and calcineurin). However, little is known about the dynamics of how CaM targets process the Ca2+ signals to generate appropriate biological responses in the heart. We hypothesized that the different affinities of CaM targets for the Ca2+-bound CaM (Ca2+-CaM) shape their actions through dynamic and tonic interactions in response to the repetitive Ca2+ signals in myocytes. To test our hypothesis, we used two fluorescence resonance energy transfer-based biosensors, BsCaM-45 (Kd = approximately 45 nm) and BsCaM-2 (Kd = approximately 2 nm), to monitor the real time Ca2+-CaM dynamics at low and high affinity CaM targets in paced adult ventricular myocytes. Compared with BsCaM-2, BsCaM-45 tracks the beat-to-beat Ca2+-CaM alterations more closely following the Ca2+ oscillations at each myocyte contraction. When pacing frequency is raised from 0.1 to 1.0 Hz, the higher affinity BsCaM-2 demonstrates significant elevation of diastolic Ca2+-CaM binding compared with the lower affinity BsCaM-45. Biochemically detailed computational models of Ca2+-CaM biosensors in beating cardiac myocytes revealed that the different Ca2+-CaM binding affinities of BsCaM-2 and BsCaM-45 are sufficient to predict their differing kinetics and diastolic integration. Thus, data from both experiments and computational modeling suggest that CaM targets with low versus high Ca2+-CaM affinities (like CaM-dependent kinase versus calcineurin) respond differentially to the same Ca2+ signal (phasic versus integrating), presumably tuned appropriately for their respective and distinct Ca2+ signaling pathways.

Histidine-rich Ca binding protein: a regulator of sarcoplasmic reticulum calcium sequestration and cardiac function.

Defects in the pathways that regulate cardiac sarcoplasmic reticulum (SR) calcium (Ca) cycling represent prime targets for driving the deterioration of function and progression to heart failure. We hypothesized that the histidine-rich Ca binding protein (HRC) in the SR may be involved in SR Ca cycling and that alterations in HRC levels would result in abnormal cardiac Ca homeostasis. In order to test this hypothesis, we generated transgenic mice with cardiac overexpression (3-fold) of HRC. Increased cardiac HRC levels were associated with impaired SR Ca uptake rates (35%) and attenuated cardiomyocyte Ca transient decay (38%), without alterations in peak Ca transients or SR Ca load. The depressed SR Ca sequestration was associated with attenuated rate of Ca extrusion via Na-Ca exchange. Triadin protein expression levels and L-type Ca channel current density were increased, while the channel inactivation kinetics were not altered. Impaired SR Ca uptake and delayed Ca decline rates triggered hypertrophy and compromised the heart's responses to increased stress by either hemodynamic overload or the aging process. By 18 months of age, cardiac remodeling deteriorated to congestive heart failure in transgenic mice. Collectively, these data suggest that HRC may be an integral regulatory protein involved in cardiac muscle SR Ca uptake and Ca homeostasis.