A Jew’s money that is deposited into the control of a non-Jew, and he lent them to a Jew with interest, if it was the responsibility of the non-Jew that if the debt is lost he [the non-Jew] would obligate himself to pay the money, it is permitted. And if it is not the responsibility of the non-Jew, it is prohibited.
Therefore, in a place where there are finance companies such, as savings banks and the like, where Jews own part of them, shares in the company, and Jews borrow there with interest, even if the managers are non-Jews, in any event it seems to me that this is totally prohibited. Therefore it is forbidden to deposit money with them, because they may lend to a Jew who is not careful. It is also forbidden to borrow from them, in case a Jew has invested in them, who is not careful.
The first part is another application of the idea that the difference between a proxy and someone who actually takes ownership being a middleman in back-to-back loans is whether the middleman accepts risk in the case of loss. See other examples in se’ifim 25 & 26.
The second part applies this principle to a corporate setting, for example, where the lender is a corporation in which one partner is a Jew. E.g. a savings bank where some of the shares are held by Jews. Since the shares held by the Jew represent a percentage of money for which the responsiibility doesn’t fall to non-Jews, a loan with interest would be prohibited.
R’ Ganzfried is clear that this is his own opinion. I am under the impression that this is not how we rule in practice. Consult your rabbi!