Cytokine release syndrome induced by immune checkpoint inhibitor treatment for uterine cervical cancer recurrence: A case report.

Cytokine release syndrome (CRS) is a systemic inflammatory condition caused by an excessive immune response and cytokine overproduction. CRS is a life-threatening condition that is often associated with chimeric antigen receptor T-cell therapy. Despite the increased use of immune checkpoint inhibitors (ICIs), ICI-induced CRS remains rare. The present study describes a case of CRS that occurred after the administration of ICIs for recurrent adenocarcinoma of the uterine cervix. A 49-year-old woman received paclitaxel, carboplatin and pembrolizumab for recurrent cervical adenocarcinoma. On day 27 of the third cycle, the patient was admitted with a fever and suspected pyelonephritis. The following day, hypotension, upper respiratory symptoms and myalgia of the extremities were noted, and the left ventricular ejection fraction (LVEF) was decreased to 20%. Multiorgan failure (MOF) occurred, and the patient received ventilator support and continuous hemodiafiltration. Rhabdomyolysis, pancreatitis, erythema multiforme and enteritis were observed. CRS was diagnosed based on elevated ferritin and IL-6 levels. Steroid pulse therapy was administered; however, the MOF did not improve and the anti-IL-6-receptor monoclonal antibody tocilizumab (TOC) was administered. Subsequently, the LVEF improved to 50%, and the patient was removed from the ventilator on day 4 and from the continuous hemodiafiltration unit on day 6 after TOC administration. The patient was discharged on day 21. In conclusion, considering that ICI-induced CRS is a rare but severe complication, fever and other systemic conditions following ICI administration should be monitored.

Association of UBE2L6 and ABCB6 Expression With Platinum Resistance in Serous Ovarian Carcinoma.

BACKGROUND/AIM: Platinum-based drugs are the standard treatment for ovarian cancer, and platinum resistance is a major problem. A previous study has reported that the UBE2L6 expression is elevated in cisplatin-resistant cells, which in turn leads to cisplatin resistance by modulating the transcriptional expression of ABCB6. The present study aimed to investigate the expression of UBE2L6 and ABCB6 in ovarian carcinoma and to evaluate the association between these markers and platinum resistance. PATIENTS AND METHODS: Ninety-two patients diagnosed with serous ovarian carcinoma (SOC) were enrolled in this study. Tissue samples were collected from these patients and analysed using immunohistochemistry to assess the expression of UBE2L6 and ABCB6. RESULTS: UBE2L6 and ABCB6 staining was positive in 41 (44.6%) and 46 (50.0%) cases, respectively. UBE2L6 expression was statistically significantly associated with International Federation of Gynecology and Obstetrics (FIGO) stage (p=0.008). Both UBE2L6 and ABCB6 were significantly associated with platinum sensitivity (p<0.001 and p<0.001). A positive correlation was observed between the expression levels of UBE2L6 and ABCB6 (r=0.673, p<0.001). Progression-free survival (PFS) was significantly longer in the UBE2L6 negative group than that in the positive group (median PFS, 31.4 vs. 11.1 months, p<0.01) and in the ABCB6 negative group than that in the positive group (median PFS, 29.6 vs. 12.2 months, p<0.01). CONCLUSION: UBE2L6 and ABCB6 expression is associated with the prognosis of SOC. UBE2L6 and ABCB6 may be potential biomarkers of platinum-resistant ovarian cancer.

Uterine Tumor Resembling Ovarian Sex Cord Tumor: A Case Report.

Uterine tumors resembling ovarian sex cord tumors (UTROSCTs) are extremely rare, occurring in less than 1% of uterine stromal tumors, and they are considered to have a low malignant potential. Due to the small number of cases, no standard treatment has been defined. A 77-year-old woman with postmenopausal bleeding was admitted to our department. Imaging studies revealed a substantial mass around 30 mm in size on the anterior uterine wall. A total hysterectomy and bilateral salpingo-oophorectomy were performed for further diagnosis and treatment. The tumor revealed histopathological findings of a sex cord-like growth pattern in the form of fascicles, cords, or small nests. Immunohistochemical findings revealed that the tumor cells were positively reactive to alpha-SMA, calretinin, CD99, estrogen receptor, and progesterone receptor, collectively diagnosed as UTROSCT. No recurrence was observed over 12 months after treatment. We experienced the treatment of UTROSCT, an extremely rare tumor that occurs in elderly women. Although most cases of UTROSCT have a benign clinical course, several cases of recurrence and metastasis have been reported. It should be followed up for a long term after treatment.

Retrospective analysis of prognosis using the Gynecology Oncology Group score of stage IB-IIA node negative uterine cervical cancer after radical hysterectomy and trachelectomy.

There is currently controversy regarding the criteria for low and intermediate risk of cervical cancer (CC) after surgery. In the present study, the Gynecology Oncology Group (GOG) score was used to detect intermediate risk. Adjuvant radiotherapy was applied in the case of a GOG score >120. The present study aimed to evaluate the validity of the recurrence risk classification using the GOG score for stage IB-IIA node-negative CC. All cases of stage IB-IIA node-negative CC who underwent radical surgery between February 2007 and December 2015 were retrospectively reviewed. The GOG scores were determined from clinical and pathological findings and accordingly, subjects were divided into 4 groups: A, ≤40; B, >40 and ≤70; C, >70 and ≤120; and D, >120. Overall survival (OS) and recurrence-free survival (RFS) curves were generated using the Kaplan-Meier method. The log-rank test produced an estimated P-value by comparing the OS and RFS of group A (low-score group) with those of others. The present study included 61 patients (mean age, 47.82 years; age range, 22-76 years) and the median follow-up was 79 (39-149) months. Of these, 60 patients were observed for at least 60 months. During the follow-up period, the OS and RFS rates of group C were 94.7 and 84.2%, respectively, while those of group D were 100 and 91.7%, respectively; the OS and RFS of groups A and B were 100%. Log-rank tests for all OS and RFS indicated no significant differences compared to group A. It was indicated that a GOG score ≤70 does not require adjuvant therapy; however, a GOG score >70 requires consideration of adjuvant therapy based on the risk factors which constitute the score.

Long-Term Tocolysis With Magnesium Sulfate as a Risk Factor for Low Bone Mass: A Case Series.

Pregnancy and lactation-associated osteoporosis (PLO) is a disease caused by vertebral compression fracture, and it is characterized by low back pain during pregnancy or the postpartum period. However, it is difficult to predict and prevent PLO prepartum in high-risk groups. Recently, long-term tocolysis with magnesium sulfate (MgSO4) has been reported to be associated with PLO. The purpose of this case series was to assess postpartum bone mass after long-term tocolysis with MgSO4 and accumulated doses of MgSO4. We report the case of a pregnant woman with vertebral compression fractures during pregnancy following long-term tocolysis with MgSO4. We investigated whether long-term tocolysis with MgSO4 was a high risk factor for PLO. Therefore, we retrospectively evaluated bone mineral density after delivery in nine women who had long-term tocolysis with MgSO4 (more than 8 days) for treatment of threatened preterm birth at our hospital from January 2020 to December 2020. The age of the women was between 20 and 41 years (mean age, 30 years). The body mass index of the women was between 18.1 and 25.4 kg/m2 (mean 20.0 kg/m2). Three women had a positive smoking history, and none had a family history of osteoporosis. The average duration of tocolysis with MgSO4 was 11 - 97 days. The accumulated doses of MgSO4 were between 168 and 3,756 g. Four of nine cases were diagnosed with low bone mass of young adult mean (YAM) value ≤ 80%. Of them, one case (accumulated doses of MgSO4: 1,260 g) was diagnosed with PLO of YAM value ≤ 70%, and one case (accumulated doses of MgSO4: 3,756 g) was diagnosed with bone fracture with a YAM value of ≤ 70%. Long-term tocolysis with MgSO4 may be suggested as one of the risk factors of PLO. Nutritional guidance and rehabilitation are important interventions for target patients.

Prognostic significance of intra-tumoral budding in high-grade serous ovarian carcinomas.

Intra-tumoral budding (ITB) has been well demonstrated to be an independent risk factor for adverse outcomes in colorectal carcinoma. This study investigated the prognostic significance of ITB in high-grade serous ovarian carcinomas (HGSOCs). The medical records and slides of 84 SOCs, including 13 with neoadjuvant chemotherapy (NAC), were retrospectively reviewed. The histopathologic examination with scoring of p53 expression showed them to be 80 HGSOCs and 4 low-grade serous ovarian carcinomas (LGSOCs). ITB was found in 64 (80.0%) of the 80 HGSOCs and 1 (25.0%) of 4 LGSOCs. The presence of ITB in HGSOC was significantly correlated with a higher level of CA125, an advanced 2014 FIGO stage, the presence of Lymph node metastasis, and the presence of lymphovascular space invasion (LVSI). The median progression-free survival (PFS) was 18 months in patients with HGSOC with ITB and 36 months in patients with HGSOC without ITB (P = 0.006), and their median overall survival (OS) was 50 months and 60 months (P = 0.060). The multivariate analysis revealed that ITB was not an independent prognostic factor. ITB is a cost-effective prognostic indicator for patients with HGSOC and ITB in ovarian tumor tissue is considered a useful histological biomarker of the progression of HGSOCs.

Difficulties in Differentiating Hypertensive Disorders of Pregnancy With Polyarteritis Nodosa.

Polyarteritis nodosa (PAN) is characterized by medium- or small-sized artery vasculitis with vessel wall inflammation and necrosis of muscular arteries, commonly presenting with fatigue, fever, weight loss, and joint pain. PAN in pregnancy is rare and is associated with worsening of vasculitis after delivery, resulting in myocardial infarction and heart failure which frequently lead to maternal death. We report a case of hypertensive disorders of pregnancy (HDP), which is difficult to differentiate from PAN. A 27-year-old multigravida was diagnosed with PAN 4 years prior after experiencing fever and lower extremity skin rash. During her PAN remission, she conceived her second pregnancy and opted to discontinue PAN medication and declined antihypertensive medications. At 22 weeks of gestation, her blood pressure was elevated to 200/100 mm Hg without proteinuria, for which she was admitted to our hospital. She was diagnosed with HDP-chronic hypertension without PAN recurrence due to the absence of PAN-specific skin or joint symptoms according to the PAN diagnostic criteria. Antihypertensive medication was administered. At 30 weeks of gestation, her blood pressure was poorly controlled and she developed proteinuria, which led to a diagnosis of superimposed preeclampsia that necessitated emergency cesarean section delivery. After delivery, her blood pressure was immediately controlled using antihypertensive medication. Our case report highlights the importance of carefully managing HPD as a serious complication of PAN.

Hypersensitivity Reaction to Carboplatin in Gynecologic Cancer: A Case Report and a Review of the Literature.

A combination chemotherapy of paclitaxel plus carboplatin (TC) is the most frequently used regimen for gynecological malignancies. As long as it is effective, a carboplatin-containing combination chemotherapy is used for every relapse. This implies that the number of platinum administrations and the frequency of hypersensitivity reaction (HSR) increase as the prognosis improves. When a patient develops HSR to carboplatin, we have three options: 1) desensitizing and continuing to use carboplatin, 2) switching to other platinum drugs, or 3) changing to a non-platinum drug. Here we report an experience of an HSR to carboplatin in a patient with recurrent uterine carcinosarcoma. The patient was treated by surgery and TC therapy initially, resulting in no residual disease. The patient relapsed 18 months after the completion of the first-line chemotherapy and was treated with TC therapy again as second-line. An HSR to carboplatin occurred at the 10th cycle of TC in total. We replaced the carboplatin with cisplatin. A chemotherapy including cisplatin and adriamycin was repeated without further HSR. We reviewed the literature regarding HSR to carboplatin and in this paper we summarize the management for dealing with it.

Strategies for the Treatment of Cervical Cancer with Bulky Pelvic Lymph Nodes: An Overview of the Current Evidence.

Cervical cancer commonly metastasizes first to the pelvic lymph nodes and then subsequently spreads to distant organs, making lymph node metastases the most significant prognostic factor in cervical cancer, and the strategy for its treatment directly influences prognosis. This review focuses on the treatment strategies for cases of cervical cancer with bulky pelvic lymph nodes. Concurrent chemoradiotherapy is the standard treatment modality for patients with pelvic lymph node metastases, but it is inadequate for bulky pelvic lymph nodes. Accordingly, surgical resection of the bulky lymph nodes has been attempted, and its therapeutic significance has been reported. If the bulky lymph nodes are unresectable, definitive concurrent chemoradiotherapy is performed. If it yields an inadequate degree of lymph node shrinkage, boosted radiation should be considered. The addition of chemotherapy after concurrent chemoradiotherapy has also been reported to be effective in patients with lymph node metastases and is currently being evaluated in clinical trials.

UBE2L6 is Involved in Cisplatin Resistance by Regulating the Transcription of ABCB6.

BACKGROUND: Cisplatin is an important anticancer agent in cancer chemotherapy, but when resistant cells appear, treatment becomes difficult, and the prognosis is poor. OBJECTIVE: In this study, we investigated the gene expression profile in cisplatin sensitive and resistant cells, and identified the genes involved in cisplatin resistance. METHODS: Comparison of gene expression profiles revealed that UBE2L6 mRNA is highly expressed in resistant cells. To elucidate whether UBE2L6 is involved in the acquisition of cisplatin resistance, UBE2L6- overexpressing cells established from cisplatin-sensitive cells and UBE2L6-silenced cells developed from cisplatin- resistant cells were generated, and the sensitivity of cisplatin was examined. RESULTS: The sensitivity of the UBE2L6-overexpressing cells did not change compared with the control cells, but the UBE2L6-silenced cells were sensitized to cisplatin. To elucidate the mechanism of UBE2L6 in cisplatin resistance, we compared the gene expression profiles of UBE2L6-silenced cells and control cells and found that the level of ABCB6 mRNA involved in cisplatin resistance was decreased. Moreover, ABCB6 promoter activity was partially suppressed in UBE2L6-silenced cells. CONCLUSION: These results suggest that cisplatin-resistant cells have upregulated UBE2L6 expression and contribute to cisplatin resistance by regulating ABCB6 expression at the transcriptional level. UBE2L6 might be a molecular target that overcomes cisplatin resistance.

Crystal Structures of the Putative Isocitrate Dehydrogenase from Sulfolobus tokodaii Strain 7 in the Apo and NADP+-Bound Forms.

Isocitrate dehydrogenase is a catabolic enzyme that acts during the third step of the tricarboxylic acid cycle. The hypothetical protein ST2166 from the archaeon Sulfolobus tokodaii was isolated and crystallized. It shares high primary structure homology with prokaryotic NADP+-dependent IDHs, suggesting that these enzymes share a common enzymatic mechanism. The crystal structure of ST2166 was determined at 2.0 Å resolution in the apo form, and then the structure of the crystal soaked with NADP+ was also determined at 2.4 Å resolution, which contained NADP+ bound at the putative active site. Comparisons between the structures of apo and NADP+-bound forms and NADP-IDHs from other prokaryotes suggest that prokaryotic NADP-IDHs recognize their cofactors using conserved Lys335, Tyr336, and Arg386 in ST2166 at the opening cleft before the domain closure.

Expression of N-Acetylgalactosaminyltransferase-6 Is Related to Expression of Cell Adhesion Molecules in Endometrial Cancer.

BACKGROUND: The aberrant glycosylation of mucin type O-glycans is thought to be associated with functional alteration of cancer cells, including adhesive properties, as well as their potential for invasion and metastasis. Positive expression of N-acetylgalactosaminyltransferase-6 (GalNAc-T6) may also be a marker for aberrant O-glycans in carcinogenesis. We previously reported that over-expression of GalNAc-T6 had a strong association with endometrial cell invasion ability in vitro. MATERIALS AND METHODS: This study investigated the relationship between GalNAc-T6 expression and cell adhesion molecules in 218 endometrial carcinomas by immunohistochemistry. RESULTS: Expression of GalNAc-T6 was found to be significantly related to expression of E-cadherin. Positive expression of GalNAc-T6 was significantly associated with better histological grade and good clinical prognosis of patients, but positive E-cadherin and ß-catenin expression were not significantly associated with improved overall survival. CONCLUSION: GalNAc-T6 might be related to cell-cell adhesion in the early phase of cancer invasion in endometrial carcinoma.

Expression of Polypeptide N-Acetylgalactosaminyltransferase-6 in Epithelial Ovarian Carcinoma.

BACKGROUND: The family of polypeptide N-acetylgalactosanimyltransferases (GalNAc-Ts) are important factors in glycosylation in carcinomas. The purpose of this study was to investigate the clinical significance of GalNAc-T6 and its correlation with the prognosis of epithelial ovarian carcinoma. MATERIALS AND METHODS: A total of 150 patients with epithelial ovarian carcinoma were enrolled and the relationship between GalNAc-T6 expression by immunohistochemistry and long-term survival was evaluated. RESULTS: The expression of GalNAc-T6 was positive in 57.6% (34/59) of those with serous carcinoma, 85.3% (29/34) in mucinous carcinoma, 15.6% (5/27) in clear cell carcinoma, and 44% (14/25) in endometrioid carcinoma. In a Kaplan-Meier analysis of patients with grade 1 or 2 serous carcinoma, the 10-year overall survival rates were 47.4% in the GalNAc-T6-positive and 9.1% in the GalNAc-T6-negative groups (p=0.047). CONCLUSION: GalNAc-T6 expression in epithelial ovarian carcinoma was different according to pathological type. In low-grade serous carcinoma, GalNAc-T6 expression may contribute to improved long-term survival.

GalNAc-T6 in the relationship with invasion ability of endometrial carcinomas and prognostic significance.

O-glycosylation in the field of carcinogenesis has been a critical topic of concern for several decades. The abnormal function of enzymes catalyzing the first step of this process, named polypeptide N-acetylgalactosaminyltransferases (ppGalNAc-Ts) has been determined to play an important role in cancer development and metastasis. Accordingly, we investigated the expression of GalNAc-T6 in endometrial carcinoma and evaluated the relationship between invasion characteristics and the cellular level of GalNAc-T6. The results suggested that positive GalNAc-T6 expression is significantly associated with histological grade of tumors and myometrial invasion characteristic. In vitro experiments showed that the over expression of GalNAc-T6 had strong association with the decrease of endometrial cell invasiveness. Taken together, our data support the use of GalNAc-T6 as a potential indicator of good prognosis and noninvasive tumor in patients with endometrial carcinoma.

Microcystic stromal tumor resected by laparoscopic surgery.

We report a case of microcystic stromal tumor (MCST) resected by laparoscopy. MCST is a very rare ovarian tumor with distinctive microcystic features and a characteristic stromal tumor immunopheno-type. The present case was a 26-year-oId woman who underwent laparoscopic surgery for suspected endometrial cyst of the left ovary. The mass was 8 cm in size and contained bloody fluid, and after attempting cystectomy, we eventually performed left salpingo-oophorectomy with a final postoperative pathological diagnosis of MCST. Although MCST has not yet been associated with malignancy, there are reported links to mutations in the ß-catenin gene, and long-term prognosis is still unknown. As MCST resection by laparoscopy has not yet been fully described in the literature, the current case provides an example of when an unexpected, potentially malignant mass is encountered during routine cystectomy and details its subsequent management laparoscopically.

Lovastatin induced Kruppel like factor 2 (KLF2), Kruppel like factor 6 (KLF6) and Ras homolog family member B (RHOB) genes and preferentially led to viability reduction of Cisplatin-resistant cells.

It was reported that statins, inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A reductase that are used to prevent hypercholesterolemia, have antitumor activity in several cancers. In this study, we investigated the cell viability of statins in Cisplatin-resistant HCP4 and PCDP5 cells compared with their parent Hela and PC3 cells, respectively, and found that HCP4 and PCDP5 cells were 37-fold and 18-fold more resistant to Cisplatin but 13-fold and 7-fold more sensitive to Lovastatin by cell proliferation assay. Lovastatin induced the apoptosis of HCP4 cells more rapidly and to greater extent than in Hela cells as assessed by flow cytometry and western blotting analyses. The MVA pathway was not involved in this acquired Cisplatin resistance. To elucidate the mechanism underlying the reduced viability to Lovastatin, we performed cDNA microarray analysis and identified 65 and 54 genes that were induced more than 2-fold by Lovastatin in HCP4 and PCDP5 cells, respectively. Of these, only three genes, KLF2, KLF6, and RHOB, were commonly induced between HCP4 and PCDP5 cells. These mRNAs were strongly induced by Lovastatin with transcriptional regulation in HCP4 cells. Consistent with transcription, the protein expression of RHOB also was induced by Lovastatin. The induction of these genes was associated with cell cycle arrest and apoptosis. Combination treatment with Cisplatin and Lovastatin resulted in an agonistic effect in Hela and PC3 cells and an antagonistic effect in HCP4 and PCDP5 cells. These results suggest that statins might have the potential to overcome Cisplatin resistance as single-agent therapy.

Crystal Structures of Two Isozymes of Citrate Synthase from Sulfolobus tokodaii Strain 7.

Thermoacidophilic archaeon Sulfolobus tokodaii strain 7 has two citrate synthase genes (ST1805-CS and ST0587-CS) in the genome with 45% sequence identity. Because they exhibit similar optimal temperatures of catalytic activity and thermal inactivation profiles, we performed structural comparisons between these isozymes to elucidate adaptation mechanisms to high temperatures in thermophilic CSs. The crystal structures of ST1805-CS and ST0587-CS were determined at 2.0 Å and 2.7 Å resolutions, respectively. Structural comparison reveals that both of them are dimeric enzymes composed of two identical subunits, and these dimeric structures are quite similar to those of citrate synthases from archaea and eubacteria. ST0587-CS has, however, 55 ion pairs within whole dimer structure, while having only 36 in ST1805-CS. Although the number and distributions of ion pairs are distinct from each other, intersubunit ion pairs between two domains of each isozyme are identical especially in interterminal region. Because the location and number of ion pairs are in a trend with other CSs from thermophilic microorganisms, the factors responsible for thermal adaptation of ST-CS isozymes are characterized by ion pairs in interterminal region.

Crystal Structure of the 11-cis Isomer of Pharaonis Halorhodopsin: Structural Constraints on Interconversions among Different Isomeric States.

Like other microbial rhodopsins, the light driven chloride pump halorhodopsin from Natronomonas pharaonis (pHR) contains a mixture of all-trans/15-anti and 13-cis/15-syn isomers in the dark adapted state. A recent crystallographic study of the reaction states of pHR has shown that reaction states with 13-cis/15-syn retinal occur in the anion pumping cycle that is initiated by excitation of the all-trans isomer. In this study, we investigated interconversions among different isomeric states of pHR in the absence of chloride ions. The illumination of chloride free pHR with red light caused a large blue shift in the absorption maximum of the retinal visible band. During this "red adaptation", the content of the 11-cis isomer increased significantly, while the molar ratio of the 13-cis isomer to the all-trans isomer remained unchanged. The results suggest that the thermally activated interconversion between the 13-cis and the all-trans isomers is very rapid. Diffraction data from red adapted crystals showed that accommodation of the retinal chromophore with the 11-cis/15-syn configuration was achieved without a large change in the retinal binding pocket. The measurement of absorption kinetics under illumination showed that the 11-cis isomer, with a λmax at 565 nm, was generated upon excitation of a red-shifted species (λmax = 625 nm) that was present as a minor component in the dark adapted state. It is possible that this red-shifted species mimics an O-like reaction state with 13-cis/15-syn retinal, which was hypothesized to occur at a late stage of the anion pumping cycle.

Crystal structures of the L1, L2, N, and O states of pharaonis halorhodopsin.

Halorhodopsin from Natronomonas pharaonis (pHR) functions as a light-driven halide ion pump. In the presence of halide ions, the photochemical reaction of pHR is described by the scheme: K→ L1 → L2 → N → O → pHR' → pHR. Here, we report light-induced structural changes of the pHR-bromide complex observed in the C2 crystal. In the L1-to-L2 transition, the bromide ion that initially exists in the extracellular vicinity of retinal moves across the retinal Schiff base. Upon the formation of the N state with a bromide ion bound to the cytoplasmic vicinity of the retinal Schiff base, the cytoplasmic half of helix F moves outward to create a water channel in the cytoplasmic interhelical space, whereas the extracellular half of helix C moves inward. During the transition from N to an N-like reaction state with retinal assuming the 13-cis/15-syn configuration, the translocated bromide ion is released into the cytoplasmic medium. Subsequently, helix F relaxes into its original conformation, generating the O state. Anion uptake from the extracellular side occurs when helix C relaxes into its original conformation. These structural data provide insight into the structural basis of unidirectional anion transport.

Crystallographic Study of the LUMI Intermediate of Squid Rhodopsin.

Upon absorption of light, the retinal chromophore in rhodopsin isomerizes from the 11-cis to the trans configuration, initiating a photoreaction cycle. The primary photoreaction state, bathorhodopsin (BATHO), relaxes thermally through lumirhodopsin (LUMI) into a photoactive state, metarhodopsin (META), which stimulates the conjugated G-protein. Previous crystallographic studies of squid and bovine rhodopsins have shown that the structural change in the primary photoreaction of squid rhodopsin is considerably different from that observed in bovine rhodopsin. It would be expected that there is a fundamental difference in the subsequent thermal relaxation process between vertebrate and invertebrate rhodopsins. In this work, we performed crystallographic analyses of the LUMI state of squid rhodopsin using the P62 crystal. When the crystal was illuminated at 100 K with blue light, a half fraction of the protein was converted into BATHO. This reaction state relaxed into LUMI when the illuminated crystal was warmed in the dark to 170 K. It was found that, whereas trans retinal is largely twisted in BATHO, it takes on a more planar configuration in LUMI. This relaxation of retinal is accompanied by reorientation of the Schiff base NH bond, the hydrogen-bonding partner of which is switched to Asn185 in LUMI. Unlike bovine rhodopsin, the BATHO-to-LUMI transition in squid rhodopsin was accompanied by no significant change in the position/orientation of the beta-ionone ring of retinal.