PREreview of The hexokinase “HKDC1” interaction with the mitochondria is essential for hepatocellular carcinoma progression

This paper explores metabolic reprogramming in Hepatocellular carcinoma via a novel hexokinase-containing domain 1 (HKDC1). There is over dependency of cancer cells on glucose consumption and this forms the popular therapeutic pathway. Hexokinases catalyse the rate-determining step in glucose metabolism. There are different isoforms of hexokinases, among which hexokinase 1 is ubiquitously expressed in all cell types and Hexokinase 2 is absent in adult tissues. However, in certain cancer types including HCC, HK2 is overexpressed. In cancer, mitochondrial dysregulation is prevalent. Both HK1 and HK2 bind to mitochondria and also alter their functionality. In midst of all this, the authors have previously discovered the 5th novel Hexokinase, HKDC1 that is over-expressed in HCC. The paper talk about the HCC progression through HKDC1 action on mitochondria.

The authors show that HKDC1 is overexpressed in many cancer types and is also upregulated in HCC. This is followed by stage-wise progression of HCC correlated with the expression of HKDC1. However, in Fig 1B, the correlation is lost in stage 4 and no explanation is provided. Commenting on this would be useful for the audience. In Sup 2B, the HK3 isoform is absent, the authors are requested to comment or add the HK3 data. This would provide an overall picture of Hexokinase’s role in HCC. In fig D, Nash+HCC data addition in a combined western would add more value.

The authors proceed for relative HKCD1 levels in the different HCC cell lines. In Supp Fig 2b and c, the western blot and qPCR data except for HepG2 are not shown. 

The liver-specific knockdown of HKCD1 and its constitution experiments are very neat. In Fig 3c and d, though there is an increase in liver size in reconstituted HKCD1 KO mice, the difference in BrdU and Ki67 positive cells is not significant. Why did liver-specific KO and reconstitution be more significant? Commenting on this will engage the audience.

The study continues to understand the role of different isoforms of hexokinase in the liver and its effect on overall activity in case of a knockdown. It’s seen that HKCD1 ablation doesn’t affect the other hexokinases. However, the addition of control siRNA hexokinase activity in Fig 4B would substantiate this more effectively. More context on the HKDC1-directed metabolism changes should be focused on. Knock studies gave an understanding of metabolic changes that would happen if the HKCD1 was targeted. Reconstitution studies of it should be included in order to grasp the complete aspect of HKCD1-induced changes.

For the mitochondrial binding, in Fig 5A quantification of the graph would further emphasize the points.HK2 data is not provided in Supp Fig 5A.

In fig 6E, the overexpression of full-length HKDC1 restores the mitochondria III activity but not the complex I activity. The author should rectify the statement in the main text.

Overall, it is a great paper that can be summarised as an identification of HKDC1 as a potential target for the treatment of HCC.